I hate to say it, but if I could afford a ventrac or a steiner and some of it's attachments, I would be selling my Gravely stuff too.
Well how much does a new Ventrac 4500K and mower deck sell for?
How much would a new 20-G sell for if they still made them?
A G series tractor, deck and snow plow was an $8500-$10,000 investment 20 years ago.
I suspect the Ventrac is similar after adjusting for inflation, maybe a little more. It is a slightly larger class of machine.
And the Ventrac represents a different approach - great for some peoples needs, not necessarily so for everyone's needs.
The Ventrac is a great machine, but I'm not sure it would do my chores any better - my chores mainly include cutting a landscaped acre and plowing snow from a paved 7,000 sq ft driveway.
Someone with more land to tend, or bigger chores to do may well find some newer technology machine like the Ventrac more effective.
I don't know what kind of GRAVELY equipment you have, or what you paid for it, or if you bought it new or used.
But I suspect in the big scheme of things, buying a new GRAVELY in whatever year, and buying a new Steiner/Ventrac in whatever year, represent similar capital investments when adjusted for inflation.
I bought a new GRAVELY 16-G in 1996, it was a big investment, but it has lasted 19 years so far,and I hope to get another 19 years service from it.
Had I bought a Steiner/Ventrac, I would have a similar view of its useful life.
The tractor in question here is an early 20-G, likely pushing 30 years old, only a close examination would tell if it is an "easy" restore, but $300 is a fair price in any case.