Have you considered going medium format with a Mamiya 7 or Mamiya 6? Or one of the fuji's (eg GSW670 / GSW 690)? While a little bigger than 35mm rangefinders, their size isn't that daunting. And it will give you something a bit different to your current set up. Most of these will come in well under budget. The Mamiya 7 could be under budget depending on the lenses you want.
If you're not too sure if a rangefinder is for you, maybe start off with something fun. A Canonet QL17 won't break the bank and will give you some retro coolness. (Plus, maybe they'll increase in value when Canon releases a 40th anniversary FF digital version later this year?) Until recently, I had a Yashica Electro 35 GSN. This is a great little camera, too. There are a lot of different fixed lens 35mm rangefinders around and they can all produce stunning photos.