Since it already has baseplate installed, if it does have the lube pump then it could make a great towed vehicle. Do you know if it already has a brake system installed?
Checking on the steering lock is simple. Just turn the wheel without putting the key in the ignition. If it turns more than an inch or two, the there is no lock. If it does have the locking wheel, then you will need to leave a key in the ignition when towing.
Check with your bank for a NADA used car price book. Most banks will show it to you. Price the car without adding for the towing equipment. The dealer won't likely find a ready buyer that will want that stuff. Make the best deal you can with out letting the dealer add on for the baseplate and lube pump.
On the other hand, if it does not have a lube pump, I would look for something else that is towable with mods. Putting a new lube pump is very expensive.
Before you buy it, have the towing equipment inspected by a reputable RV repairman to make sure it is all working as expected. He can tell you if it has any kind of braking system installed.