The trap won't add $15 in material costs. The point is that if you
cut the old trap off, and then put in a new PVC trap, you can then use a
more modern base that's very easy to install.
The trick is getting the trap set in such a way that the riser hits
dead center of the drain.
If your shower opening is a standard size, then you could even put
in a pre-made base, which is easier yet.
From the way your talking, though, you might need some expert
on-site advice. If you're brave, you could tackle it yourself, and then
call in someone if you failed. It wouldn't hurt to try.