I was kind of hoping we could get a community project going (after 250 views), but I am glad you are willing to at least look at it.
David contacted me via email (he is out of town and on dial-up right now) and said when he returned to town he would try to get involved also. He told me he had looked into some of this at one point already (so he might have a head start).
As for which GOS unit, it kind of depends on any given day what is least expensive. You have the 4400, 4200, 4500, 15000, 18000, 110, 210, 410, and 520 to choose from (I am not sure a 110 or 210 would be a good idea for this project though). There are others, but they are usualy rare and/or very expensive or kind of "quirky". I am guessing a 4400, 4200, or 4500, maybe even a 410 would be the least expensive. Just depends on any given day. I have seen them all sell for way too much and also seen some really good deals.
As for the GOS, I am sure we could get one up to the latest 5.x GOS
Give us/me an idea of what you want and area of price range and I can do some looking for you.