Sorry, that makes no sense. For around $1200 you can buy an 1RU supermicro with 6-core i7, 32G Ram etc. that will smoke your mini ($1500, 4 cores) on every metric. If your rackspace is precious you could fit two of them into one RU with a half-sized case or by leaving out the case altogether (not much more esoteric than stacking mac mini's imho).
I love the mini (I have one under my desk!) but suggesting apple consumer gear (including the apple tax) would be a cheaper alternative to generic x86 consumer-gear is a little nuts.
Well, "good" is a relative term when you use a non-ECC board for a server. ;)
I just summed up the component prices for similar servers that we have built - that's the ballpark if you are willing to assemble it yourself (takes around 45mins when you're not doing it the first time).
I can get a MicroCloud chassis for $500 per server (x8), with the rest of the hardware working out to around another $700-800 per node (x8 again). Slightly lower density, but not too bad.