What's the cheapest all-tube Marshall?

I'm looking to buy a Marshall amp (I've been playing on a friends, and it sounds so great). I'd like to buy one that uses only tubes to amplify, with no solid state or mixed amplifiers. However, I don't need a huge amp, and I don't want to drop too much cash on this (I know that Marshall amps aren't cheap). My question is this: What is the cheapest all-tube Marshall amp I can buy? It doesn't have to be a combo amp, but if it's just a head I'd like the price of a Marshall cabinet included. Wattage isn't terribly important, although I'd prefer something above 15 W.