>>How easy is it to tear apart auger drive assembly
Depends on the make and model. The front ends are mostly similar and fairly simple. A simple bolting arrangement holds the front end to the tractor base. The belts come off and the bucket separated from the tractor section. May have to undo a cable or spring.
The auger drive is just pulleys and bearings driving a rod into a gearbox. The pulley at the back of the intake housing comes off, the auger shaft bearing supports on the bucket sides come off to allow the auger gearbox, auger drive shaft and impeller to all slip out as a unit. Once out, the auger rakes come off and gearbox can then be opened.
Most machines are about like that but the difficulty is with rusted parts making the job difficulty increase significantly depending on what’s frozen and how bad. Without rust problems the job is fairly easy and can be done by most people. Get the online parts breakdown and keep notes or take pictures as things are taken apart. Aside from rust bucket work is straight forward.
>>and drive wheel gear box assembly
Can be difficult depending on the machine and what’s to be fixed. Not many have “gearboxes”. Are using that to refer to the box between the wheels as a whole? If a real gearbox then possibly you are referring to a Toro PowerShifter. Those are not for the homeowner or even someone with a bit of experience. Just swapping one out whole is a task and not for Joe Sixpack.
>>Also how much is a 20 year old 10hp Tecumseh engine that runs well actually worth ??(not burning any oil)
W/WO electric start? Around Boston 20-150. For a rusted “don’t blow smoke” motor 20. For one with good paint, good compression known by testing and desirable, 100-150 depending on the model.