Taken in the inseam and taper the jeans are two completely processes.
Your tailor can do two things. If you don't want to lose the selvedge, they can open up the out seam and pull the the sides out to create the taper, but then you end up with a really wide selvedge line. Or they can cut it and re-sewn which you'll end up lose the selvedge lines.
It is possible to taper on the inseam, not just the outseam. Most specialized denim tailors taper this way. It might not come out exactly the same as tapering on the outseam, but it actually works well.
I could only find a pair of raw black SPURR selvage, how's the quality of their denim for $60? Edit: How's the quality of NFY by Notify jeans? They seem to be the cut I want (straight with a slight taper) and only $50