Rebecca,
For more money, I’m partial to the VW Sportwagen. However, like you, my budget was much smaller than that. Hubby and I purchased a 2006 Pontiac Vibe last fall. It fits my 52″ lever harp in the back seat, with plenty of room for an 70 pound dog in the way-back.
The back seat folds down flat, so you may be able to fit a pedal harp in that car. We paid $7000 for a Vibe with 106k miles; I suspect we could have gotten one in similar condition for less if we didn’t just want to get the car shopping thing over with ASAP.
GM shut down its Pontiac division, but the Vibe is well-known to be a Toyota Matrix with a different name slapped on it. Parts and repairs are still easy and affordable to obtain from your local repair man or from Toyota (if you let dealers near your cars. We don’t 🙂 ).
Good luck with your search!