I currently use a single M series PLC so I don't have the demand to support the development. But I see this as a unique opportunity for Tri-PLC to provide a new feature no other vendor currently offers.
The PDA's not only offer increased memory, but the purchaser could use the product as a permanent or portable HMI unit. These hardened products incorporate the buttons and touch screens to operate controls as well as memory to leverage intelligent HMI's at a fraction of the cost. If the user wishes to purchase higher end PDA's, bluetooth and wifi are now a reality. I would consider paying for this interface software far more than the direct EXCEL applet you are currently offering. It also eliminates the need for a server based on PC hardware installed local to the PLC. It doesn't make sense spending $600 on a PC that is not industrial hardened to function as a data collector when the PLC is only $200.
Who knows ... I might even consider commercializing my application if the functionality was available and I could keep the packaged costs below $500USD.