Carbon monoxide alarms......so expensive for the HOH or deaf GEE WHIZ

I will be using propane in my van for heat and cooking. So I need a reliable detector for carbon monoxide. Theres plenty out there for larger homes /families with deaf and non deaf people out there. Really in my search theres not a lot out there for single people who just want a light strobe and runs on batteries. The one that looks promising is this
 http://www.marilynelectronics.com/SafeAwake-Fire-Alarm-SAFEAWAKE-p/hc-safeawake.htm?gdftrk=gdfV23318_a_7c1154_a_7c4507_a_7cHC_d_SAFEAWAKE
Now i know you have to plug it in and yes it will cost you your arm and leg but we are talking carbon monoxide here. The silent killer..so we can't play games with this. I'll try to cut costs else where where it is NOT important.
But this is not the end. I'm still looking.