I came across a Pre B CZ 75 that was made in 1980 that I'm thinking about buying. It's in great shape with the original black epoxy finish and no import markings.

I have a couple of CZs already and was thinking about customizing this one to my sons liking if it doesn't carry any collector value.

What kind of price do these usually go for and would I be destroying its value by making it more user friendly?

Only a collector could tell you, but I would certainly not butcher it, but buy a new one that is already set up to your specs. When they were being brought in under the wire, as it were, I think they went for four figures, but that was scarcity. If I had any scratch, I'd buy it off ya. :)

Thank you for your input. I may just try and trade it for a 75B to someone that has an interest in collecting.

Personally, I just like to mod a gun like I want it and shoot the snot out of it.

I have no problem changing this one up to my sons liking as I don't care about resale value. I just hate to ruin it for someone that does.

The are some rare models and configurations, without seeing the gun, it's hard to guess. Imported ones in rough to worn cosmetic condition sell for $300-$400 regularly. 

Good condition non-import marked 1980 gun is worth quite a bit more than a new CZ-75B. Mods would be needed to make it a carry gun (stock, the mags don't drop free, for example), and the mods would decrease the collector value.

To give you an idea, this one just sold for over $700, plus shipping, on GunBroker.

http://www.gunbroker.com/item/629014952

It is a 1986 in solid used gun condition. Your 1980 would be worth about the same, ceteris paribus.

However, if it is in the Short Rail configuration like the original 1970s CZ-75s, then it would be worth quite a bit more. These usually go for $2,700 and up import marked and there would be a premium for non-import-marked, as the vast majority of the non-marked ones (like my first CZ) were bought by US GIs in the European Rod & Gun clubs, and personally imported on an ATF Form 6. ISTR that 1980 was the transition year from short to long rails but I'd have to check my references.

(I'm working on a book on Czech and Czechoslovak handguns)

If you do want a long-rail, pre-B CZ-75, CDI sales is selling the last of a large amount imported recently from Israel. They're selling 'em on GunBroker and they're going for $350-600 depending on condition. These were police and range-rental guns and most of them are pretty well beat up.

For carry, a newer gun is better. I retired my old CZ for a Glock for a couple of years but now am carrying a CZ-75 P-01, a compact 75 with alloy frame and rail, and a decocker in place of the "cocked and locked" safety. I have come to really prefer the decocker as I always carried hammer down anyway. With a CGW trigger it's almost too good to carry! It's "compact" compared to a full size 75, about the same size as a Glock 19, not a 26. Hand fit is much like the big guy, but it's shorter (14-round mags). I like it.

You can save a lot of money with the new polymer guns, the -07 and -09.