You should be able to find a Kurt Kinetic new on sale or used on Craigslist now that the winter is over. People will start to dump them. The KK trainer is so highly recommended because of its consistency and high build quality.

To stay on topic, my experience with indoor training reflects that of the OP. I did two of the base programs and then started in on the build. My outdoor riding was every bit as fast as where I left off last fall and my endurance is better. The indoor training is so effective that I plan to continue using it for the rest of my build program interval sessions. Outdoor rides will be for endurance, fast group rides, and just-wanna-go-for-a-ride rides.