HMA, I can make you one using this schematic:
http://www.pdp-11.nl/viperpit/altimeter/altimeter.html
It's relative low-cost, the mosfets are € 5,- per piece, the CD4047 something like 65 cents..
The transformer is the kicker at € 25,- or so.
This one can go to 25W using the small heatsinks but up to 100W using large heatsinks on the FETs.