I have used those Digi modems and they are not bad, $21 for each node gets you wireless serial cable or wireless GPIO. These are much better, for $35 you get a

I have used those Digi modems and they are not bad, $21 for each node gets you wireless serial cable or wireless GPIO. These are much better, for $35 you get a wirelessly connected little computer that let you download and run Python scripts.