Flaig's was a large custom gun shop located in Millvale PA. They ran text-heavy ads in most issues of The American Rifleman from the 1950s into the 1970s. I've seen ads from the mid-60s featuring the FN actions. Because the 7mm Rem Mag was introduced in 1962, your rifle was produced or at least barreled after that date. In the early 1970s Flaig's were using Ferlach Mauser actions; some of those rifles carried iron sights, although the FN-actioned rifles were not advertised with them. The barrels on the FN rifles were often made by Douglas.
Presumably by "fixed sights" you mean the barrel-mounted open sights. The connotation of "fixed" is usually "non-adjustable", and most open sights of centerfire rifles are adjustable.
Brownell's will have a selection of sights suitable for the rifle. You might consult with your gunsmith before ordering, because matching sight heights front and rear can sometimes be a non-trivial exercise.
Value? Do searches on AuctionArms, gunbroker, and other sites. Don't overlook the completed auctions, and remember that asking prices are frequently high on ads for unsold pieces.
Good advice, and a good posting.
I'm now in the search for info on Charlie Flaig himself. Not much I can find on him. Lots on his Hunter's Lodge however.
I visited his store many times when I lived north of Millvale, and saw his fine German rifles and shotguns he sold, plus those magnificent Ajax scopes, with the monster objectives.
Also, I never learned what happened to those fine drillings, etc, after he died, which I think was around 1980, +. or -. I know he was 86 when he died after a fall the broke his hip, or leg, not sure which.
I know that his right hand man, Bill Knabel, ran the Lodge until about 1988, or 1989 when it closed for good. Last I heard was Bill was working in a gun shop up Rt.19 in Wexford. Bill would know what happened to all of those old Drillings that were once owned by the Nazi elite, including Herman Goehring. I saw all of those Drillings one time.