I ran miata wheels on my CRX for a number of years. Actually, three different sets.
The miata wheel was 54.1mm...the CRX was 56.1mm. So I was in the same boat and had to have them machined.
A local machine shop charged $10 - 12 per wheel. For the second and third sets I bumped them up to 56.2mm. The 56.1 was just a little too tight.
That's a great price on those wheels...almost too good to be true. Most Mugen stuff is waaay too expensive. I thought there was only one legit Mugen importer in the US. On top of that, there are a ton of knockoffs out there. Not saying that is the case here, but it certainly pays to be cautious.