If budget is a big factor, you may be able to find a used factory navi for a semi-decent price (~$400), but you have to be VERY careful about what unit you buy, because there were three different navi units that all look exactly the same, with the same connectors, but only work for certain applications (sorry I don't have part #'s for you.):
Non-Bose trucks and SUV's (very rare - I've only seen one in my life)
Bose trucks and SUV's
Centerpoint Bose for trucks and SUV's

The problem you will run into is that if the seller doesn't list them properly, they are NOT interchangeable. If you got a Bose version, you will need to jury-rig an amplifier (very difficult, even for us to do) and the Centerpoint unit won't work at all, no matter what you do because it communicates with the Centerpoint amplifier via data, not analog audio outputs.