One alternative to vintage or boutique amps is the Fender Blues Jr. Here is a site that I just saw on Harp-L that goes through a bunch of Modifications to make this little amp sound better including some tube swaps that will help it sound great with harp.
Bill's Blues Junior Modification Pages "Fender's Blues Junior is a great little amp--it's small, light, priced right, and all tube. It has spring reverb, flexible tone controls, and it's loud for its size. It has a couple of shortcomings, however, that can be overcome without too much difficulty."
