I think it would be hard for you to find a GS w/o navigation. There are some out there, but like the LS, most of these vehicles are equipped with a navigation package. To answer your question about price, you need to provide more info (e.i. mileage, color)
There are some 08 GSs w/o nav for sale on Autotrader in the $32-33 range. $28 for an 07 is a decent deal.