If you are not opposed to an aluminum one have look at a Griffin Radiator. They are not cheap either, but I think a good bit less than the Walker one.
http://www.griffinrad.com/I don't have any personal experience with them, but I have never heard anything bad about their products. I did call and ask a few questions, and they seem very helpful and friendly. I'll most likely be buying one for my 48 when the original gives up, or can't do the job.
Grigg
