I made something like this
I’ve written a PocketPC app for my ipaq on windows CE 2004 that tracks market data (auctions from the typical auction site feeds) as well as street-sales data (tracks my sales, and i can enter prices i see advertised on the street very quickly). This is great, because i can factor the per unit cost of my current inventory, and have an interface where i can see my inventory, my costs, current market trends, and suggested selling price for a material or item all on one screen.
It also stores mining locations and data, and i am working on the map part for the pocket pc, it’s taking a while because i want to have a vein analysis tool as part of it, to help decide where to bomb next for veins. All of this data is replicated to my laptop using SQL replication, but using a SQL site over the net, i can can have this data shared with all of my soc mates.
This is not yet ready to be released to the public, and I am working on coordinate ↔ image pixel location mapping for Amethera and some other features previously stated.
Perhaps I will create a SQL site on the internet and allow societies to have thier own SQL instances of this application, so only thier members have access to thier data, but i think i would need to be able to support more handheld platforms, as this is written in the Dot.Net Compact Framework.
I can handle the application versioning & updates, and data storage for a small amount of Peds as a monthly fee for each society, with unlimited users for each society.
Also, the installer works nicely, and the SQL Schema is created on your handheld automatically when you do your first replication to the SQL site.
I’ve found in this project that creating the backend and basic libraries was easy, the hard part was making a great UI that made sense, was simplistic, but also provided all of the data one would want when making trades, or analyzing mining spots. Also, dynamically writing icons and markers onto a handheld map was easy, the hard part was the behaviours that handle what to do when one of these markers is clicked, because the markers are written directly into the bitmap in .net, i had to go back and look up what was written onto that location based on the coordinates and current query scope for the mining spots displayed, so there was alot of de-bugging to get it right.
Good luck with your project, and if there are any idea’s you want to bounce around, or get input on, I’d be glad to post more about this topic, i find it very fascinating to see all the tools that can be built to make life in PE more automated.
One of the most disappointing parts about programming for PE is finding that the network packets are encrypted, so I could not grab data that indicated that i hit a mining spot, could not intercept the current location, say if I hit the key to display the current coords, and could not derive a whole host of information that could be entered into a DB automatically if I could cap the packets.
I am thinking of using voice data entry to handle this, because as any miner knows, jotting coords on paper and doing data entry is tedious, but simply repeating the coords, and having the handheld verify the coords verbally back means you never have to take your eyes off the screen or ALT-TAB into another app to do your data entry. The iPaqs are totally suited for voice detection using contextual voice commands, and verbal verification, where it repeats it back to verify what you said.
Well, my coffee is wearing off, time to hit Starbucks, GL,
Reminds me of this:
Would love to have an online edition in java, or at least runable in linux so I can use it on another comp as I play.
And even help you with some programming if you want to use VB. 
