If you just need to receive an SMS but don’t actually need a cellular network, Google Voice is free.
If you can stomach $3/mo + tax (totaling a little over $40/year), UltraMobile PayGo is the cheapest consumer option I’ve seen. It’s a T-Mobile owned MVNO. It comes with 100MB, 100 minutes and 100 text messages per month, and is pay as you go after that.
Still too high for a phone number I expect to get an sms per day.