Connect Anywhere

I understand that I can purchase a SIM card from AT&T for $2 plus postage. Then purchase data for 500KB for .99 for 30 days. More data amounts is available or if you exceed what you purchased they just automatically charge another 30 days worth. All I want to do is be able to check that the A/C is running because we leave the dog at the rv. We have unlimited on our phones and tablet for anything else. Has anyone connected that can give me an idea of how much data to purchase?

I can’t imagine it would be more than a few hundred MB a month.