How much should I expect to pay an attorney to draw up a purchase agreement for a small franchise purchase?

It is difficult to answer this question from the limited information provided. In addition to preparing the contract, your attorney should be expected to review the franchise agreement and take steps to assure that the franchisor consents to the sale to you, and that the franchise agreement will be, after closing, in force and default-free. Likewise, your attorney needs to review the lease and make sure that it is transferable and confirm the absence of any defaults. This process might cost several thousand dollars.