My husband's a 25B. Because of really great ASVAB scores and a perfectly clean background (so he was eligible to get top secret clearances), the recruiters bent over backwards to get him on, promising him extra college funds beyond the GI Bill and a 20K sign on bonus (payable in pieces over the 6 years he had to sign up for, plus 2 years of inactive duty after)...but this was back in 2007 and they weren't getting many people that were qualified signing up, and they really needed those spots filled. Where he's at in Baghdad, it sounds like there are too many 25B so a lot of times they also end up pulling guard duty and that sort of stuff, but since he's been gone a while we're not familiar with the current demand state-side, and we don't know anything about Afghanistan yet. It never hurts to ask a recruiter...just don't sign anything until you've gone through every letter of the contract and it states exactly what you want. Even then, they'll find ways to complicate things...
with that being said, the GI bill is an option, i suggest taking it. while you are on active duty you have tuition assistance so you dont have to use your GI bill or pay out of pocket. you wont find out about any sign on bonus until you go to MEPS. the recruiters can sometimes ballpark it but its not guaranteed until you go to MEPS and sign the contract.
unfortunatley there is no such thing as a demand for state-side or anywhere else. its about how many people are already in that MOS. it also depends on where you go. ive seen many different people in many different MOS's doing jobs other than what they signed up for. thats part of being in the army. youre a soldier first, your MOS is secondary.