I agree with all of what
MrPhil says, but I just wanted to add something. I actually find it somewhat fishy that someone (or a company) is charging
only $145 to set up an e-commerce site which generally takes a lot of work to do. Just be weary.
Also, if you decide to do it yourself... I've used osCommerce to make a book store site of around 100,000 or so books. It's not the easiest to maintain (OK, it's a downright pain to maintain [especially if you're synchronizing the records from a physical store's database]), and it doesn't have the easiest learning curve, nor the prettiest interface (backend or frontend), but it gets the job done. Fortunately, though, you have a few more options than just this. I recommend you take a visit to
this site and try some e-commerce shopping carts out for yourself to see if any of them suit your needs. Some of these open source shopping carts have large communities that support beginners and can help out with any problems you might run into.