Any minute now Scott's gonna get on here and tell you to get a remote
starter switch. Using one is a quick way to tell if the problem is more in
the starter itself or in the wiring. It would be best to do that after
you've cleaned the transmission ground or added your ground strap; you can
use a jumper cable (much common sense required) to bypass the main battery
cable if you really think you need to.
IIRC I just hooked mine up to the terminal on the back of the alternator.

The worst part of getting the auto starter out is the upper bolt, imo, but
it's not really that big of a deal. Somewhere in the archives there's a
description of how to use a multimeter to test each key point of the wiring
from the ignition switch through the safety switch and on back (from David
B., maybe?). If you've never gone through the system and cleaned/inspected
it, it would be worth a few hour's work to do it- if it's never been done it
needs it anyway and it can help in that a big part of this problem, I
believe, is often the cumulative effect of a number of degraded contacts.
The ends of the wires to the solenoid on mine were pretty messed up and from
what I've read that's pretty common.