Compressor purchase

and what about to make your own?

1337,

Not really. When you consider that the silent compressor with care will last you 10 years or more I don't think it's a bad deal at all. It is a lot up front but I would guess that many people have 5 times that amount of money in unbuilt kits in their stash.
Now the Medea Shark compressors like you mentioned are the "High-roller" types, especially since they start at $495 and go up to $1095 for the Great White Shark T-shirt compressor.
Speaking of the Shark series compressors, here's a Hammerhead Shark model for sale on Ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=28111&item=8112027517&rd=1&ssPageName=WDVW

Mike

Mike, that's highroller/big spender!

How about a Badger Million Air?
It is basically the same as the Silentaire 20A and is a little cheaper.
That is if you want to spend $400 on a compressor.

Mike

silentaire 20a is more expensive, but really really quiet
maybe a silentaire scorpian 1/2 or iwata sprint/smart/powerjet

if you're a highroller/big spender, maybe one of those "shark" compressors