Guy-Fast

There a fair price. You cant run a batch of a 1000 so you run batches of maybe 50. Takes 3 months to sell them at maybe a 15-20 dollar profit. Hence why its not the best idea. You will sadly be better off making a missing link and selling them on ebay.

HiProfile

The guy posted his original idea for this on HT IIRC, but maybe HMT as well. Story goes he wanted the adapter made, but it would be just a tad more to make a bunch, vs the high cost for just one. In other words, its like a personal group-buy. You could easily have 50 of these made for very little, assuming you didn't have it perfectly CNC'd, your logo cut into it - just a few simple cuts and deburring the sharp edges.

If you really want to do something cheap - either look at the motorola/freescale 2.5/4bar map mod thread, or try the non-ported versions. Before they started selling the ported 2.5bar's, I got the free-air style, and made little aluminum cacoons for them. I was thinking of even going with glass-filled epoxy for some mini-production scale numbers, but then they started selling the ported ones again, as well as the "free"scale sample thread popped up...

I do have to say its the only cheap way to get a 7bar sensor (freescale MPX5500D) to work...