A pre-Model 25 will cost you over $800 for one "new in box" according to Supica, but expect to pay at least $200 to $400 more because they are so scarce in mint condition. These guns should be "5-screw" models.
A Model 25, .45ACP will cost at least $550 (4-screw) or $400 (3-screw) if NIB, but expect a premium for a complete gun, box and all papers.
Collectible guns include the M25-1 variant, any of the 100 mismarked ".45 CAL. MODEL 1950" on the barrel or a variant with a factory 5" barrel. Older guns (pre 1969) have an "S" prefix to the serial number.
The 1955/Model 25 in .45 ACP is a sweet shooting gun. Mild recoil and very accurate. These were also made in .45 Colt caliber (M25-5) starting around 1978.