A dart Block will run you around 4500 to 4900 plus shipping
The two blocks list below are a much nicer block for around the same price.
Donovan splayed 4 bolt / Donovan is out of California
www.donovanengineering.com
New Century 6 Bolt / New Century out of Illinois
http://newcenturyperformance.com/Index.htm
Both around 5000-5500
If you chose a donovan block and can't seem to get a deal less than 6 grand let me know I have bought a few of them and I get a little better pricing
Check out the web sites