To be clear, the FR-7 has a "bent bolt" or turned down bolt handle. The FR-8 has a straight bolt handle. The FR-7 is less desirable than the FR-8 because the 7 is a small ring Mauser originally chambered in 7 X 57. Many consider the FR-7 to be unsafe to regularly fire 7.62 X 51 NATO ammo and VERY unsafe to regularly shoot full power .308 Winchester US commercial ammo, especially the Hornaday "Light Magnum" ammo.
The 8 is "probably" SAFER as it is a large ring Mauser originally chambered in 8 X 57.
Remember, all of these rifles are built with used military receivers and should be considered "suspect" until properly inspected by a competent gunsmith.
And, I would not give a dime over $250 for an FR-7
The FR-8 Special Purpose's you'll find will be in 7.62x51 -- people, I think reasonably, pass on the small-ring Mauser FR-7 all the time. If you were going to use only relatively mild factory ammo it might be fine but at that price I'd CERTAINLY pass it by.