Is it a lot of trouble to install a driver's side door key lock or do I have to take it into a shop

Not sure what you mean by the "keyhole" is missing. The keyhole is integrated with the handle. Depending on the tire ... the rim will run about $200

if the lock cylinder is missing from the door handle they are actually really easy to replace once you take the door handle out. They are held in by a slide clip and are easy to install. However there are two problems with this 1. you have to get a new lock cylinder that is keyed like your others (done by locksmith or dealer) or replace all your locks with a new set including ignition which is expensive, or just have a different key for that door. 2. If it is missing its not likely to have been taken out. Instead it was probably knocked out by a thief who broke into the vehicle. There is a common problem where they knock the lock out which breaks the retainers on the handle, then they grab the metal rod and unlock the door to get inside. This breaks the handle as well. Common problem and their are aftermarket safeguards for it. I can't remember what it is called but its a metal plate that bolts to the backside of the handle inside the door. This would be a good question to post on the dakota-durango.com forum. I used to be a member on there. Sorry I can't help further. As for the spare tire and rim, that site is a great way to buy one.