Indy - this may help you.
I bought an Epiphone Valve Junior a couple of years ago but I was never truly happy with the tone. The circuit is a bit naff. So I got Martin at Martamp to tweak it for me. He changed the output transformer and tweaked the basic circuit as best he could, plus I swapped the speaker for a Celestion Super 8. It was OK, but still a bit ragged. It was limited by the standard circuit of the Valve Junior.
So...............
One trip to Martin and I now have a winter project which consists of:
* Valve Junior Combo box
* Celestion Super 8 speaker
* Valve Junior chassis, stripped of the circuit board and new valve socket holes added
* A Ceriatone Tweed Champ circuit board
* A bunch of parts - valve sockets, nuts, bolts, valve caps, cable etc
* A soldering iron and some fresh solder
* A circuit diagram
That's one route you could take, using a Valve Junior or the Harley Benton equivalent from Thomann, and some parts/diagrams from Ceriatone (plus other sources).
Other than that, you could contact Nik at Ceriatone directly for a quote on a Champ combo. He's going to be the cheapest 'fully built' option:
http://www.ceriatone.com/productSubPages/AC5F1Champ/AC5F1ChampComplete.htm