I agree with Nasty 135, that must be one heck of a tiller he is trying to sell you. You can do a lot better than that. That's about what my 50" Kuhn tiller cost about 4 years ago.
If you are going to use a tiller to put in a garden, it has to work pretty hard to break up the soil for the first few times you use it but after that it's fairly easy work. Start slow and shallow, about 2" or 3" and work your way down to full tilling depth in 2 or 3 passes and you will be in good shape. The more compost you add, the better your clay soil garden will be but it doesn't take long to get it producing. Since you're breaking new ground, it might help to get a soil test done. Your local extension agent will be able to help.
You'll love that tiller. If you have a big garden, it's an amazing worksaver. It's so much easier on the body and faster to sit on a seat and let the tractor do the work than to fight with a walk-behind.