That price sounds a bit high. There is currently some concern about whether Browning will continue the line or not and I think that is inflating the prices on Hi-Powers... if they don't you can probably find a Hi-Power at a better price. If they do, you will probably see the value of that one drop to less than what you would be paying.
As an older Hi-Power, it will have more value to a collector of Hi-Powers (providing you can find one). In the condition you describe, it might be worth $625 to a collector but plan on holding on to it awhile until you can find an interested party.
Check out
www.fnhipower.com for a serial number list and good info on the gun.
The other value in the gun is that it is a "Belgian" Hi-Power that is made and assembled in Belgium. The newer Hi-Powers were made in Belgium but assembled in Portugal where labor was cheaper - these are considered less valuable by purists (collectors). However, FN has discontinued assembly in Portugal and the latest pistols are once again "Belgian". If Browning continues to produce the gun for a few more years, that may cut into the collectors value of yours.
As far as parts go, check out the link above. Different years of production have different variations. In some cases it is as minor as the hammer, sights or safety. In others, it may effect the extractor, disconnect safety, etc.
Whatever year of Hi-Power you own, you should be able to find plenty of surplus parts for it.