All the major manufacturers are producing 4 stroke skis now, and I'd recommend them over a 2 stroke especially for a beginner, even if you buy a used ski. You will also want to look at 3 person skis if you plan to do any towing.
You might be surprised that the prices for skis have not dropped that much with the recession.......seems to be the same with boats, and sales right now are strong. Unfortunately, this is also peak season and probably the worst time to buy if you are looking for a new ski. The best time to buy a new (or used for that matter) ski is between October and April during the off season for the best price. Don't be surprised if dealers don't budge too much on price right now. You will get better deals at the winter boat shows when they are trying to clear last years models.
Probably the best deal on a new ski right now is with a Honda, since they have stopped production of skis (at least temporarily), and dealers are clearing their inventory. You can find new 07 model F-12s and F-12Xs (turbo model) for around $6000 without a trailer. Of course, there are fewer Honda dealerships, you have to wonder about availability of parts and support down the road if Honda decides to drop PWC production permanently, and the Honda turbos require a little extra maintenance.
Next entry level option in price would be a Yamaha VX at somewhere between $7-8.5K for a new one. This is the ski you will find at 75% of ski rentals due to its stability, easy to ride, and very reliable and proven design.
Kawasaki has several nice skis in the $8-9K range, but the do not enjoy the reliability of the Yamahas. It may also be harder to find a local Kaw dealership in your area.
SeaDoo skis tend to be the most expensive, but will also come with more gadgets and accessories. SeaDoo skis use a closed loop cooling system, which might be a plus if you are running the ski in salt water most of the time. All the other brands use the water the ski is running in to cool the engine, which makes for an easier to maintain system, but with the increased possibility for corrosion if the cooling system is not flushed properly after salt water use. In part due to the increased complexity of the SeaDoo brand, the closed loop cooling system, and possibly since they tend to have more add-ons (like brakes, suspension, etc.), the SeaDoos tend to have more maintenance/repair problems than other skis.
Skis, boats, cars, are pretty much all the same.........once you drive it or tow it off the lot or dock it automatically looses 10-20% of its value. If you take your time you can find lightly used skis with low hours for $1000s less than a new one. Many will still be under warranty.