Too big? You did take a look at the pic? This is probably the smallest card that has ever been made for the A1200.
Price-wise, I may be able to offer something even cheaper if I can get cheaper CPUs. There's a bunch of 68EC020FN16 CPUs out there, and I could change the design of the ACA1221EC to use the FN package. If I can get hold of enough CPUs, that is (otherwise a production run would not make sense). Such a card would come with about the same CPU power as the A1200, so it would aim at ACA500 users only.
The "few minutes" that you're quoting for soldering a chip quickly add up to a whle hour if you take into account that the card must be shipped, packed/unpacked, tested and worked on manually. A technician's hour is at least 60,- EUR plus VAT, so you easily exceed the price of the ACA1221 if you let the business gain a few EURs (after they have added a share of the standard monthly cost that you have just for running the business "idle"). You can't compare hobby-prices to an official offering by a company that you (as a customer) want to hold responsible for warranty, after-sales service and *maybe* even further developments for your favourite computer.