not sure what is the monthly pricing of this developer sim card. Here in Germany, i use fonic/congstar prepaid sim cards from the super market for 10euro's which comes with 10euro balance. These prepaid sim card's have a data plan of 100MB/30days for just 2Euros. In my xmpp based raspi-IoT solution 100MB per month is sufficient - hence my running cost of this IoT setup is around 2Euros/month.