Four stroke engines are more reliable, and do use less gas. Unlike 2-stoke engines, which use oil, 4 strokes do not. It is more like your car engine. Put oil in to lubricate the moving parts, and it only burns gas. After so long, change the oil and add in fresh. Gas and go, thats about it. In 2 strokes, you have to fill the gas tank and there is a tank for oil. It burns them both, so instead of just putting in gas, you have to refill the oil too. After a day or so, the prices start to add up.
The seller is trying to rape you by selling those for 12.5K. DO NOT BUY THOSE FOR THAT PRICE. Depending on condition and amount of hours, fair price for those, (figuring average condition i.e., a few scratches, and with a fair amount of hours for those years, i.e., around 60 or so) would only be about 8K for both. Maybe 9K if the skis and trailer are in really good condition and there are about 30 hours on each ski, and there are OEM Honda covers for both skis. Covers are pretty expensive new. For example, the one for my Kawasaki lists for $365. Again, I think that 8K is a fair price for those two. Has the maintence been done on them? Have they been used in saltwater? Is the engine bay clean? How many hours? Excessive hull scratches? All the keys to the machines? All of those things affect the price.
If you don't need two skis, check out some Honda dealers. Most Honda dealers still have some F-12/X and R-12/X models from previous years in stock. Some of them will be leftover 06's, I've even seen some leftover R's that were 05's. They will usually give you a better price on the older skis, but they are still brand new with 0 hours. I was offered an 05 R-12X without a trailer for $5,100 once. Before I got my Ultra 250X, I almost got an 06 Honda F-12X with trailer, 3 lifejackets, cover, anchor, and a 4 year warranty for $9,000. It was brand new with 0 hours, but it was an 06 and it was 2008. Check out some of the dealers and see what they are offering. The stock of leftovers should be dwindling now. You may have to drive further to get a ski, but it will be cheaper than others and it will be brand new. For the $12,500 the other guy is asking you could probably get a new 05/06 R-12X and 06 F-12 if you look hard enough. You will have the R-12X Turbo for a go fast fun craft, and the F-12 for long cruises.
Some Hondas do have the reboarding ladder already attached. Most didn't, but you can buy the OEM Honda one to install yourself. Remember, to install one you have to drill into the hull. If you don't feel safe doing that, there are other options. One option is a "rope style" ladder. It is like rope material that is very thick. It attaches at the tow loop at the back of the ski and falls into the water. Its just as easy to use, but you have to remove it or tuck it in everytime you get ready to take off. You get a better picture of what I'm talking about at overtons.com Thats where they sell them. It will also be cheaper than the OEM one.
The Honda skis are okay cruisers, but not the best. If the waves start to pick up, it won't be the smoothest ride. Especially not the R-12X. I've also heard that the Honda skis splash alot too, but I haven't experienced that, I've just been told. If you do end up getting a Honda, there is a splash deflector that fits on the front to deflect splashing water. You can buy them at overtons.com If you are looking for more of a cruiser, the Yamaha FX may be a better ski. There is a natural aspirated model that makes about 140 horsepower. It is the base model, so I'm not sure if has the reboarding ladder and such. The higher model is the FX H.O. which stands for High Output. It makes about 165 horsepower, and would be the equivalent of the Honda F-12X. It doesn't have a supercharger or turbocharger, and will probably use less fuel than the F-12X but it will be a close race. Both skis will probably be the same on acceleration and top speed. Both skis are pretty good on fuel. If you are looking for more of a cruiser and just want a fun ski, I wouldn't worry about the F-12X or FX H.O. I would instead look at the regular Yamaha FX and Honda F-12. They will still be fun to play on, but will get better gas mileage than the others. Both of those are known to have long fuel ranges. If you can deal with a little bit of a slower craft, check out the Yamaha VX. It has a smaller engine than the FX and only makes about 110 horsepower. It is not speed demon, but it probably has the best cruising range of any PWC on the market. It will still be fun to play on, but it doesn't look as good as or faster than the FX or F-12/X. There are even "cruiser" versions of the FX and VX. They have a unique seat that has a mini back support. The FX has more features that make cruising better like tilt steering. Save yourself some money and buy a regular FX and just buy the seat from a cruiser model. It should fit and gives you the better seat without buying the entire cruiser model.
From what you've said it seems your more interested in a cruiser. The Honda's will probably be more fun, but won't be as comfortable on the long cruises. I would lean more for the Yamaha FX or VX. Both are 3 seaters. If the regular FX isn't fast enough for you, go for the FX H.O. You can buy the cruiser seat for the FX or VX if you get those. But, if you could get a leftover Honda for a really good deal, it may be better to get a Honda. The Yamaha's are going to be higher in price. To get a Yamaha for the same price as a Honda, your going to have to buy used, unless you get a VX. Cliff notes:
Best cruiser = Yamaha FX or VX
More fun = Honda F-12X or R-12X
Uses least amount of gas = Yamaha VX
Fastest = Yamaha FX H.O. ties with Honda F-12X
Slowest = VX
Cheapest = Honda
Best features = Yamaha
It just comes down to a bargain (leftover Honda) vs. a ski that has more options (Yamaha)
Happy to answer any other questions...