Frequently, PIS's can be found on eBay or amazon.com NIB (new in box) for deeply discounted prices, as well as the accessories. Occasionally, big stores like Babies R Us will have good coupons for Medela products.
If it's primarily a $$ issue, I would check into getting a single pump only if you're planning on pumping infrequently. They run up to $60, but again, you can use the discounts or websites above to save even more money. If it's to pump to go back to work or if you plan on having more breast-fed children, a nicer system may be worth the investment.
If you can get your hands on the book Baby Bargains, I would do so. It contains money-saving tips across the board, and breast pumps are no exception! It was and still is an invaluable source of information for me.