I bought a chassis kit from Andy / Saturn, glad I did. I can't comment on anybody else's product from a first hand point of view but all those previously mentioned have consistently good reviews. I have a soft spot for Spud and Handy as I like the way they conduct their business and themselves. I didn't bother looking for cheaper once I was happy with what I was getting.
Enoch.
PS you can see it going together at my web site -
www.deepfolly.co.uk. The chassis pack is one of Handy's the side panels and nosecone are the Saturn ones. I think they are somewhat spendid