25-100
Could have been Erma, Rohm, RG, Sauer or any of a half dozen others.
25-60 USD or so
erma made alot of guns, alot under military contract to make other guns like lugers and p 38's. any differences from the luger will only be aesthetic
This model was manufactured from 1973 to 1978 by Erma Werke in West Germany for Ithaca.
50 dollars
Best left to a gunsmith.
You specifically have the Iver Johnson TP-25 pistol. These were produced on US-made frames from the Iver Johnson location in Jacksonville, AR with internal parts produced by Erma-Werke in Germany. Your gun was produced in the late 1980's.
You did not say which model. The Erma-Werke KGP68, which looks like the traditional "Luger" pistol, is about $250-$500, depending on condition. If you have a different model, please repost with that information.
10-100 USD or so
The Targetmaster Slide Action, made by Erma in 1985, books at $175 in 100% condition.
What is the value of an ERMA Werke kgp 68 9mm ?
Not much. This kind of small cheap imported single-action .25 caliber automatic is often called a "Saturday Night Special." I'd guess the value is about $75 if it works and is in fair to good condition.