Hop on Craigslist and search your area for "electric wheelchairs".
Now the wheelchair that you decide to buy will determine a lot about how easy or difficult the next couple of steps will be. If you are looking for an adventure, buy any old wheelchair you see in your price range and saddle up for a few hours or days of troubleshooting and hacking.
If you'd like to make things a bit easier on yourself, buy a wheelchair that you can test and make sure it works. If the wheelchair's batteries are dead or don't hold a charge, don't worry about it as that's an easy replacement. The unit should however power on, not give any trouble codes
, and drive around. If it does these things, load it into your car and take it back to your cave.
and I purchased 4 wheelchairs in one day a few months ago and spent an average of $150 - $250 per wheelchair that met these requirements. Some even came with fully functioning batteries!
Bring ramps for your car or truck if you can, and drive the wheelchair right inside. It will make life easier. Otherwise, bring a friend and do some heavy lifting.