If you only have 4-5 days, i'd concentrate on Moab and Monument Valley. In Moab, you could easily spend the entire time just doing Arches, Canyonlands and Dead Horsepoint. However, as Monument Valley is only around 2-3 hours south west of Moab, i would not miss out on that either.
You can see some of my galleries for both at the following addresses:http://www.pbase.com/kssphotography/moab_uthttp://www.pbase.com/kssphotography/monument_valley
You do also have the option of heading ne from Moab to Captial Reef and Bryce but if you only have 4-5 days, spending 4 days in Moab and 1 in MV is probably a better way to maximizing your shooting time. There are of course numerous other places in Norther Arizona and southern Utah (Zion, Page, GC, Escalante, Coyotte Buttes, Sedona), but like i said, the two closet locations from CO are probably Moaba and MV.
I think the next time i goto Moab, I'm going to try and devote 5-6 days to Arches alone, as there is just so much to see there and you only have so many sunsets and sunrises on a short trip.
I think Arches can also be a treat in April, if there is some rain before you get in, as you have the oppertunity to get some nice reflections - something, i haven't been lucky enough to experience during my 5 trips there. I've only gone there once in April and while i did have some good clouds a couple of photographers who had gotten in a week before i did said they were able to get some amazing reflections when they got there at the start of April.
there are plenty of fairly cheap motels in Moab (between $50-80/night).
Check the following:http://www.discovermoab.com/hotels.htm
I personally prefer staying somewher where they have at least a small fridge, to store cold drinks.
As far as MV, there are some cheaper motels in Mexican Hat (25-30min away fromMV), but I'd recommend staying at Gouldings as it is closest to the park, which makes it easier to get out for sunrise.