I wouldn't take advice from someone who can't spell simple four letter words. As a ten-year raft guide who has worked on the Ark and the Poudre I think you're getting yourself into something great! The energy that comes with showing people the best day of their year is amazing and you'll constantly be amazed that you get paid for it!
Yep, you'll make between $30 and 40 for a half day and probably work 6 half days a week at first. However, you get TIPS - and I can't believe nobody has mentioned this. My average in my first year was probably $10-15 per trip and was nearly $40 in my 10th year. I know some guides that do even better than that. A six-day a week senior guide in Colorado, working for an ideal company can earn nearly $10,000 in a season with tips and pay combined - but it will take a long time to get there. Count on making about $3000 total your first summer and most of that in July and August when the water is a lot lower.
As for where to go, this topic has been debated ad infinitum so I'l stick to advice where I've worked. The Ark is fun, and has a much deeper, richer guide culture - but Brown's Canyon is really easy and the work usually ends in mid-August. If you're looking to camp and party all summer it might be for you. Lots of boat traffic. The Poudre is a better (much more fun IMHO) river at high water, but doesn't have guaranteed flows like the Ark can. However, in a good snow year you can earn money running the same 2 miles over and over again all the way through August, which can mean a lot of cash to a rookie. Fort Collins is a cool town, but is a LOT bigger than B.V. It's hard to camp all summer, but there is more going on than just the river.
I would suggest making a list of companies in both towns and applying after you see what the snow is looking like in February. Big snow - go to the Poudre. Less snow - maybe the Ark. Of course there is commercial rafting on the Animas in Durango, other sections of the Arkansas (Royal Gorge, etc.) and all over the U.S. so don't stick to these two necessarily - I just wanted to give advice about where I've worked.
Oh, and if you work in Fort Collins DON'T work for A1 Wildwater. The owner is SOUL-less trash and will literally trim those small paychecks so he can pay the bills on his riverside mansion. I'd recommend training with Rocky Mountain Adventures - the new owner seems great and there is a good balance of experience and youth these days.