By way of reference, I bought my 1984 C25 for $1000, and that included the engine. I'd suggest that you sell the bike and see what you can get for it, then buy the boat with the bike money. The C25 is a great first boat, but I wouldn't want to live aboard it. Weekends? Sure. Maybe even a week cruise with a significant other. But much beyond that, and she's to small. Most C25's don't have showers. Most have porta-potties. Most don't have standing headroom unless you're on the short side (my 5'4" tall wife could stand, but I couldn't) or keep the pop-top up all the time. And there are issues with keeping the pop-top up, like making sure you have the screens and windows for when it rains/is hot. Oh, and speaking of heat, most C25's don't have A/C, and you'll probably want that in the summer.
All that being said, I bet if you go over to the Catalina 25 Owner's Association (Catalina - Capri - 25s International Association
), you'll find someone who is living aboard. Take a look at his/her lifestyle. If it's for you, then maybe this isn't a bad deal. But, as others have said, beware the hidden costs (dock fees, maintenance fees, etc.).