You need to have someone who is familiar with equipment look at it and show you how to check the pins, bushing, sprockets, rails, and rollers. If the under carriage is bad It is not worth much more than scrap. A new under carriage can be $10,000.
I bought a 977H (1964) at an auction a couple months back for $5700. The under carriage was good but the little things add up. Books $200 - 1" plate to make bucket edges $50 - missing broken bucket tooth root $200 - Bucket linkage bushings $100 - 2" rod to make New bucket pins -$50 new track frame bolts $32 - new filters $85 - Reupholster seat $90 - Final Drive gasket $15 - oil 160 qt. -
Bottom of the air cleaner $? - Emergency break linkage $? - High/low range linkage $? - New batteries $150 - 1 TRACK ROLLER $250 - having it huled home $450
Luckily I have a brother that has a shop , tools, and knowledge to help me work on it. If you had to PAY A DEALER!