i wonder if anyone can help. I bent my inter 18 boom at the weekend...it is 'finito', i think. Inter 18 booms are over £400......I was wondering if a f18 infusion boom would fit on my gooseneck as they're much cheaper. I don't really mind about the lack of outhaul track etc.

Ya know the boom on my C2 isn't much more than a 2" iirc piece of Aluminum tube (1/16" wall) with a few well located holes and slots... You probably can move the hardware from your old boom. Alu tube is cheap. Find a metal supply place near you. In LA, 20'of 2" tube is about $50.00 for 1/16 wall and $65 for 1/8" wall. Shorter lengths are usually cheaper even when they charge for cutting.
Pick something about the width of what you have and use a similar wall thickness.
If you use center boom sheeting, you might want to go 2.5"

Yeah, you could annodize, but that will add a minimum of $75 or so to the cost and not make a big difference in longevity.