Gravely's are tough old hardware that will last forever! The newer ones (a relative term...) used kohler engines that you cans still get parts for. Parts for the rest of the gravely are mostly still available, but you may have to order them - don't count on your local retailer having stuff for you. I have a couple of the much older L models - one runs and the other needs transmission work - someday...
They are a handful and will give you a workout keeping them pointed in the right direction. But they will go places that no 4 wheel tractor can get. I keep mine for bushhogging spots that the tractor cant get to safely.
They used to be fairly common, but not used that much anymore so you can often find them and attachments for little or nothing (buried in somebodies field...) - but don't count on them running as is. All easily rebuildable and made to be fixed, not thrown away. Nowhere near as refined as the BCS/Grillo models, but built for heavy work. Would love to have a newer BCS, but have maybe $200 in my Gravelys, and can't get near even an attachment for the new stuff for that price! It does what I need it for and that works for me. But I also have a big 4 wheel tractor for most of the work we do....