Very Low. You cannot typically buy a working train engine. It is generally government property, and if available, only via auction when retired.
If you are looking for a or a train simulator instead, I can help find the best ones. buy a real train
If you are looking into this for a commercial project, I can look for for commercial renovations. Very Low
If you want a train, you are likely buying a static display piece for a commercial venue, not a functioning locomotive to drive around. and if available