TT,
Yeah, it is tough to find a workable compromise between performance & $ when shopping. You are right in thinking that you have the opportunity to save a bunch by buying used. Most bows offer some sort of length-of-pull adjustment. It may be as simple as changing a cam module, up to changing the entire rigging (cam(s), cables, and string). Your 31 1/2" draw also will make things a little tougher to find one you can "step into". This can be moderated a bit by your choice of release (shorter effective draw), or using a very slightly longer string. This should let you get good use out of a 30-31" bow.
What I would suggest, go to a larger, more popular, proshop in your area, even if it means some driving. They usually have any number of used bows to try, and the expertise to make any needed adjustments. They may also know who has last years top model, or even one from the year before, and is looking to upgrade. Many of them sponsor shooters that change bows as soon as the new models appear. This allows them to sell a new, top-of-the-line bow, and help out a proven customer, by selling their bow to you. They also have the added bonus of selling you the accessories you will need. They are also there to service their sales. I would caution against any mail-order, including auctions, as there is no way to inspect or try the product. You may, or may not, get what you pay for. Invest some time, and the NECESSARY cash, and this should get you off to a good start.