What it is - you can likely look up on Google or similar to read that Spanish FR7 were conversions of earlier Spanish Model 1916, some of which were conversions themselves from 1893 Models. So it should be a Small Ring Mauser - without the third safety lug on the bolt and similar gas handling issues as most other Small Ring Mausers. I believe they were made up when Spain was in process to convert their Forces to use a semi-auto in 7.62 NATO, but the design and execution of function for their CETME semi's was not initially going too well.
What it is worth - will vary with the potential buyer and condition, condition, condition - a rusted out bore versus a pristine bore? A clean, well head-spaced bolt or a bolt face severely cut up with primer gas leaks? A stock that has been replaced or an "original" one? Anything "customized" on it, or all original? There is simply not enough information given to come up with a realistic price for it.
By the way - various posters on Internet are not kidding - an original stock that has been sanded down to "look better", might cut the value in half - even if the sanding job was done 30 or 40 years ago by a previous owner. There are several examples of that here - various cartouche and stampings that were originally in the wood stock are now gone - because they were not noticed or understood what they meant or did not care about that.