I'd think 8' would be great.
Iceberg gets most everything on C-band with 6', if you read his posts.
That's a C-band only setup, and you'll need something to run the servo to change from V to H polarity (and set the skew).
... as well as something to run the motor to move the dish.
That could be as simple as an old analog receiver, but you read the site - this has been discussed weekly. -
As for the $85...
People get similar dishes for free, but have to take them down.
Here, it looks like all you have to do is take it home.
If it seems mechanically sound and not deformed, I'd think it was an adequate deal.
That dish is sure going to weigh a heck of a lot less than the 10' fiberglass in your first post! - :up
Oh, any brand info?
I'm not good with BUDs, but is that a Winegard?