[mojoB]

> As an aside, I have been unable to get my hands on any modern multi-frequency GPS receivers. If someone has a link to one that I can buy with a credit card, I would love it!

Try SwiftNav or Tersus. I have not used either of them so I can't comment on the quality, but $1-2k for an RTK setup is pretty great. They are both more 'startup' than traditional suppliers.

uBlox F9 looks good but isn't quite available yet. They have a solid line of single frequency receivers so I'm looking forward to seeing pricing.

I have briefly tested some Unicorecomm from China, and they work well, but they miss your online store requirement, and the documentation is nonexistent.