How about a 70-200 L zoom in f2.8 or f4 formats? The Non-IS versions are in the ball park in terms of price (f2.8 version is a bit pricier than either of your choices though). And, f4 might be too slow for short exposures.
I love this focal length range for widefield astro work 70mm takes in the Rho complex thru to 200mm for Eta - having that zoom range is very useful.
Garyh took out the top prize in last year's Malins with a widefield image taken with the 200mm f2.8.
Have you checked out the Astrotrac drive as an alternative to the SkyPatrol?
http://www.astrotrac.com/
All the best
Doug