Welcome back to the splash zone, David!
Regarding the water, I'd start by checking out the LFSs closest to you...in the long run, the time you will spend driving week after week will be the critical factor. I don't know the shops out east, but both Neptune's and Aquamart have quality water supplies. See if you can borrow a handheld TDS meter and check potential supplies; I can't imagine a shop not willing to draw a cup from their supply to demonstrate...well, actually I can imagine it, but I can't imagine buying from one.
For that small a tank, I'd suggest just buying the RO/DI and mixing your own saltwater when you need to do a water change--you'd only be needing 3 or 4 gallons at a time and it will give you your choice of salt mixes and probably save some money. Mix overnight in a 5 gal bucket with a power head.
Regarding rock, posting here is probably the best start. You won't need much and the hobby seems to still be following the general economy...bottoming out but still not into growth...so you'll probably find some offers/posts about tanks being torn down. That said, I think I'd also make the rounds of local shops for that as well...yeah, they'll be charging $5 to $7 per pound (vs. $1 to $2 from a hobbyist) but it will give you the best choice of rock variety, shape and size. (Plus you'll be more assured that it hadn't been dosed with copper or other medications.) I wouldn't suggest going online for that small a quantity...that makes sense (to me) when you're needing 50 or 100 pounds.
I didn't see a post from you in the Marine Aquarium Society of Colorado forum here on RC or the separate MASC website (link available as sticky post in the forum here on RC). Both are good local sources as well as D.A.R.C. and with a bit more active forum traffic.
