Well it really comes down to if you want to get faster, be able to ride longer, and increase your performance. If you only ride to be outside and like the scenery but don't care about getting faster then I don't think it's nesccesary. I got my trainer because I want to get faster and and be competitive.
I was on a tight budget like you and went with the Travel Trac fluid trainer from performancebike.com on sale for $120. It's a solid unit if you just want to get some spinning in and some workouts. It's not comparable to the Kurt Kinects but it gets the job done for about $300 less.