It is a conversion of an M1 Garand. I would stay away from it myself. They look cool but are famous for malfuntioning all the time.

I have a Fulton Arms Tanker, had it for years, it shoots great and I have had no problems with it.

If it's Springfield Armory, Inc.  Then it will be a replica of the T-26 rifle of WWII.  They're pretty well built, and I've seen several at just about $650, so the price is in line.  The SA,Inc receiver is cast, and has been known to wear out at the sight adjustments.  There's a fix for this, so it's not a show stopper.  Something to know though.  I guess they didn't cast them in the same as their M-1A receivers, as I haven't heard of this problem with them.  It is loud and short as noted.  It was made in both .308 and .30-06.

If it's a WWII Springfield Armory Garand cut-down into a "tanker", then it's probably a bit high.  Most I've seen go for $550.  You can identify these as they look a little rough.  There is no short front handguard, and you'll see the oprod between the gas cyl and the handguard.  Most have an M-14 handguard on them.  These tend to be either really good or really bad, with majority being bad.  

I'd say the SA, inc would be worth getting.  If I found one, I'd probably buy it if I didn't have anything else to buy.  I wouldn't bother buying a Fed ord, or whoever unless I was guarenteed that I could return it if it didn't work.

Ross