Adding a second CDI/GS

We have a Garmin GNS430, UPSAT SL30 NAC/COM and Sandel EHSI. I'd like to
add a second course deviation indicator/GS for when Murphy shows up and the
Sandel quits at the worst possible time.

A couple questions for the avionics gurus on r.a.o:

- How much is this going to cost? There's the cost of the instrument,
whatever switches and annunciators are needed, and maybe 8 shop hours for
installation and checkout. I'm guessing about $3k for the lot. Is that
realistic? Anything else?
- Can I switch the indicator between the 430 VOR/LOC/GS and the SL30 NAV
inputs?
- Is it very difficult/expensive (or worthwhile) to add the GPS deviation
info to the second indicator? We have an MX20 to use as a moving map while
setting the GNS430 display to CDI mode.

Thanks in advance for some free advice.