Need more pics to determine its value. I agree with a lot of what has been already said but without more info it is a guess. IMHO
Do you have a pic of the underside of the slide showing the firing pin tunnel? Is the finish of the entire gun consistent with the pics shown. Do you have pics of the magwell and are there any marking there? What color is the underside of the grips? Looks to have the internal extractor. As others have point out HP serial numbers rarely tell the entire story when it comes to early FN Hi Powers. FN reused serial numbers or used whatever serial number convention was requested in contracts or other requests.
I will say that it is not a FEG. Give me more details and I can tell you a much better WAGs then you have been given so far. If I cannot figure it out I know people who can with the right information.
From what I can see in these pics it is a pre 1962 pistol. It has the internal extractor. It has an internal extractor which was standard until 1962. At that point they changed to an external extractor but this did not mean FN stopped producing internal extractor guns in 1962. They often used leftover parts and slides after model changes. You will find guns made after 1962 with the older design.
For me personally the proof marks and inspection marks on the gun give the best info. The *M on the barrel, frame and slide is an inspection mark of Louis Couchant (1923-1952) or Maurice Scorpion (1959-1968). On first look I incorrectly guesses this was for MS but now believe it is LC.
It has the Belgian smokless proof Poudre vive of PV proof. The Lion over the PV. I also see the proof of Liga which is on FN produced pistols. It is not the combination proof which was introduced in the mid 1960s. I do not see any Belgium acceptance marks on the gun so it is a "commercial" gun.
The inspectors mark *M tells you when the parts were inspected but not necessarily assembled. IIRC. I agree with Ibmikey and others it is was imported into Germany because of the Silesia marking. The Silesia marking in the mark of the commercial seller/retailer in Germany that sold the pistol once it was surplussed.
German police forces started buying FN Hi Powers around 1951. The guns they purchased had standard commercial markings and no other identifiers. The serial number range was from 28,000 to 60,000 according to Vanderlinden. So it would appear that this gun with a serial number of 28088 was and pistol early in that run maybe even the 88th of the contract. So this leads me to believe this is a commercial FN Hi Power made between 1951 early 1952.
So that is my WAG based on what I can see. As to value it is worth as much as you can get someone to pay you for it or someone can get you to pay for it. If you can buy for $600. Buy it. If you are selling I would ask for more.