Hi Una --
The progress is exciting. Considering that a 2-piece Theory suit run ~ 500 full-price I think 500 + fabric for a 3-piece custom sounds reasonable. Though that fabric cost does add up, alas!
[To spread out the damage, you could always ask for a quote on a 2-piece but buy enough fabric for the skirt/pants to be made up in the near future.]
Are you really stuck without fabric stores in the nearish vicinity? A lot of them will have coupon deals that can *really* help keep your costs down. [I do gravitate to those 20-40/yd materials and thus do love my 40% coupons, ha!]
If not, I have another online place I've seen recommended by quality-driven blogger-sewists for service and materials (in addition to the gorgeousfabrics mentioned above):
http://www.emmaonesock.com/
In terms of what to get, given your climate and the fact you want this to wear I'd look for a 10 ounce worsted/merino wool in the 80s-110s range.
The 120s and up are silky but not as durable and (personal opinion) even lined they feel flimsier to me. I like a nice hefty drape on my backside, ha!
[I do have a few tropical wools I love in the summer, though.]
***Oh -- and this will be hard but DON'T RUSH your fabric choice! Order or bring home swatches and/or wait for the right one to show up****
I have been so cranky trying to find the "right" silk print in the right colors for a dress for a month+ (looking at hundreds of bolts) and almost settled, then finally found one I love. You will be wearing your suit for a loooong time and it is worth debating colors, weights, and textures.
Good luck!