The MiniMig costs almost nothing to make in volumes. All the R&D is done, you just find sources of the chips and a place in china to make em and churn em out. I don't think you realise what kind of markup there is on ready made MiniMig's. I think Acube probably made their money back (which is always a good thing).
While you could make an FPGA devkit with enough capacity for AGA + 020 (although no-one knows how much that would be for sure) for about the same price as todays retail MiniMig, you'd have to mark it up considerably to make viable profit.
I used to be disgusted with the markup on the MiniMig's, but once you actually look into all the costs which go with officially retailing an electronics product within Europe then you gain a lot of respect. It's not like they could just make them, flog em and split the profits down the pub. There is quite a bit of expensive red tape once you go legit.