No such weapon. You need to see a gunsmith.
No
It depends on several things. Is is new or used, what model is it, and what condition is it in?
100-400 or so
Have it examined by a gunsmith. It can be chambered for either 9mm Luger or .380 ACP
50-800 usd
NO, NO, NO, NO, !!!!!!!!!!!!!!!!!!!!!!!!! THEY ARE NOT INTERCHANGEABLE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Same thing. Yes.
S&W never made a 25 ACP handgun for retail sale.
100-600 USD depending on condition, box, accessories, papers, etc..
Different designations simply mean different things. ACP stands for Automatic Colt Pistol, meaning it was originally designed for Colt Auto Pistols, however, pistols from various manufacturers will fire ACP ammo. Other designations, such as SW in .40 SW means the cartridge was designed by Smith and Wesson. WCF stands for Winchester Center Fire. GAP stand for Glock Auto Pistol. There are various others.
Smith & Wesson made several different pistols in .45 ACP, including an M1911 pattern pistol. You'd have to be more specific about which model you had in mind before this question could be answered, as the different models vary quite a bit.