For everyone who has suggested getting the band to re-track the tune in a different key: Neither band still exists. These two versions of the same song were recorded by two different bands a number of years ago. My client doesn't want the song newly re-recorded, they want those original old recordings spliced together.
As far as how long it'll take...the edit took less than 5 minutes. If I don't bother doing any pitch transposing -- (which, if I do it, I'll definitely be subbing out, as per my OP) -- I'm gonna feel guilty about billing out my time at 1 hour. Pretty sure I can't get a 4-piece band into the studio and setup, much less mic'd up, in less than 1 hour. We're good. I've spent more time writing posts in this TB thread than I did in the studio working on this job!
But I genuinely appreciate all the input, thanks! I'll think I'll definitely check out Audacity at some point, 'cuz who can argue with free?