Hands down, IMO, the best manufacturer od custom sac's is Fly High - they manufacture Fat Sac's.
3879 N. Richards Street
Milwaukee, WI 53212
You can get a quote by completing this form
and faxing it to them.
I have two, one for each side and they are great sacs, and a great company to work with. The sacs are a bit pricey, but worth it, IMO.