I bought my receiver second hand, but in excellent condition for 12.5k. You should be able to find more than capable HK, Denon or Onkyo 5.1 receivers in the sub-20k range, easily, just don't go for the newest or top of the line models. For example, you won't need an HDMI receiver since the PS3 audio can be connected to your receiver via optical cable (and keep the HDMI or component video straight to your TV).
If you upgrade later, consider replacing your Bose satellites with better, even just entry-level bookshelf speakers. A pair of Wharfedale 9.1's shouldn't cost more than 8thou. Later, you can pair them with rear speakers, or buy pair of floorstanders for the front and then use the bookshelves as rears.
With a good pair of floorstanders as fronts, you won't even really need a sub except if you really want rumble and LFE (low frequency).
But a good receiver can last you for years, and will start paying off immediately.