Best left to a gunsmith.
If you either push or pull the barrel, there is a pin over the front of the trigger. When you push or pull the barrel on the frame that pin wil be able to slide out and you can then slide the barrel and bolt forward, then pull the pin in the knee action of the slide link and it should all come apart. Wouldn't know of anyone with a firing pin for this pistol, mine broke and it seems there are none in the world.
50 dollars
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.
25-100
10-100 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
I know of no handgun that has a one inch diameter bore.
The Targetmaster Slide Action, made by Erma in 1985, books at $175 in 100% condition.
Whenever disassembling or cleaning any firearm wear safety glasses. To disassemble the Erma ER25, place the safety lever in "safe", then remove the magazine (clip). Now pull the slide back and visually ensure the chamber is empty. Release the slide, move safety to "fire "position and with muzzle pointing in a safe direction pull the trigger to release the tension on the firing pin. Inside the trigger guard at the top us a small lever that extends past the frame on both sides- pull this downwards. It can be tight so you might want to use a non-marring tool to help. The slide with the barrel intact will now move forward off the frame. Be careful to not lose the firing pin spring and the firing pin. If they don't fall out remove them once the slide is separate from the frame and place them where you won't lose them. This is as far as you should strip the frame. Holding the slide assembly inverted you can push the barrel forward with a finger or tool and lift it at the breech end. Maintain control of the barrel as the recoil spring is under pressure. Now ease the barrel out and slide the recoil spring off the barrel. This is as far as you should strip the slide. Reassembly is the reverse of these steps. If you have trouble fitting the barrel through the front if the slide use a pencil inserted at the muzzle to help center it in the opening. This is a striker-fired pistol and as with any of these you should cycle the slide and test the operation of the trigger and safety before loading it. If improperly assembled or if the striker is damaged some of these may discharge accidentally upon loading the first round in the chamber.
25-60 USD or so
I just saw an Erma EG71 at a Canadian Gunshow in Ontario. Looked to be in really good condition. Seller said he had work done on the firing pin. Was asking $295 Canadian. April 2008.