BC,
A couple of things. First, email Greg and ask if he can ship using a USPS Flat Rate Priority Mail box. Then your shipping would be only $7.70.
Second, you may want to try and find out where the local golf courses get their fertilizers from. You may be able to get them in bulk for way cheaper using that route.
In the mean time go to Lowes or Home Depot and look for either Grants or Greenlight stump remover (it'll be in the section where they sell weed killers and stuff). Both are pure (as far as everyone can tell) KNO3. Here in CA it's about $5/lb so it's not a cheap source but it'll do in a pinch, or when you only need a small amount anyway.
For PO4 you can use Fleet Enema which Wal-Mart sells for cheap. Just make sure you get the plain enema with no perfumes or other additives. If you go this route I can give you general dosing guides.
Finally, I just purchased a 50# bag of K2SO4 from a lawn maintenance supplier so I can ship you several pounds of that in a USPS flat rate box for $7.70 if Greg will not use USPS as a shipper.