I got a really cheap wireless set from my local grocery store, (HEB) and after a year and a half it still works great! It cost about $15 I think and the range is pretty good. I can go in the house, go up stairs and sit down at the computer while watching the temp of my brisket outside! Only one probe though. Here's what appears to be the same model at Amazon.
P.S. I will add that I did have to replace the probe about six months ago but it was my own fault for having it in an over heated cooker. I was cooking on the Webber kettle and the temp got away from me.