An interesting thing here.

A display with 250x250 diodes would have 62500 diodes. If we assume $0.02 / diode, that would come to $1250. If we assume a similar sum for PCB, all latches, buffers, PSU etc (remember that a PSU supporting max 30% lit diodes at 20mA with 3.8V output and assumed 95% efficiency would need to supply 375A and 1425W and draw 1500W from mains). Then $500 for a good rain-protected box without problems with condensation etc. The cost may be $2500 to $3000 for a display.

The OP is a bit worried about a few dollars for the radio solution. A $100 GPRS solution would maybe represent 3% of the total cost. And the GPRS coverate may be a big advantage.