Fair rates for crafting professions?

I've got 450 BS and I'm trying to spin some money out of it but I'm not sure what the going rate for services are. I was thinking of setting prices based on AH profit at the time of sale: for example if someone wants an item and the AH price is 400g more than mats price, I would make them for 100/200g - so still a big discount on the markup vs buying them on the AH.

Had some discussions where other people offer flat rates though - what's the going average would you say?

Best to just advertise that you're LFW and discuss rates with people individually and agree on it. Or just buy the mats, make the thing, and take the 400g profit off the AH.