What is the best , cheapest Co2 Monitor?

Can anyone give me a suggestion for a cheap Co2 Monitor to hook up to a tank system with a regular. Cheapest one I have found is around 300 right now, anything cheaper.

I just need it to read the PPM, does not need to control anything else

C.A.P. just came out with a new monitor for 269$ but no idea if it is a well built product. I haven't been very impressed with C.A.P's stuff in the past.. When you get the $ go for the Sentinel CHHC-1
Peace

sorry clicked post! but it does the trick just fine for cheaper monitor and i've borrowed friends sentinel to compare accuracy of readings and always within +- 10ppm of the sentinel. and at only 189.00 pretty decent.