Alpine, WY? If you go there for a boating trip in mid march you could easily be snowbound. Who knows with today's weather though. I spent two summers in Soda Springs, Idaho and there is a serious lack of boating there compared to other parts of the state. Look into the Blackfoot River and Henry's Fork, but really this is not a boating destination especially during the time you are coming. The Greys is a good class IV run in spring, but I don't think it usually happens that early. If it's running it's likely CO will be thawing out too. There is also the Bear River near Grace, Idaho that has a run on it, which may go earlier due to its desert location.
I would guess that by the time you drive to Montana for Beartrap or to the Hagerman section of the Snake, and then back to Alpine you will have driven more than is prudent for said runs. Not trying to ruin your spring break plans, but if I were you I would hope something in CO goes or head down to NM.
Otherwise N. California boating is only 18 hours one way from Laramie and it will be going for sure, but this would involve a great deal of driving and you're unlikely to find a tank of gas out here for under $2 a gallon. That said you might look into paddling the Ozarks, they might be closer than California and are most certainly cheaper, but are rain dependent.
P.S. if you are in Alpine head south to Afton, WY and go drinking at Colter's Lodge. A group of us USFS interns had a beer with Harrison Ford here. He was driving his beemer down to SLC from Jackson for service. Celebrities aside, Colter's is a good, cheap place to get pickled