I don't know about the interference thing, but I have a Cateye Strada wireless and have never had any issues of that sort. I have a small LED blinky light, though not one of the big powerful ones. Usually costs a tad over your limit, but I found mine on sale for $42. Only real complaint I have it that it is too easy to accidentally reset your trip counters by leaning on it, since the entire body of the computer is the button. But it has a distance 2 that acts as a backup for trip distance. It does not have a temperature function, though.

On my mountain bike I have an Ascent IO, which is presently on sale at Performance for $29.99. http://www.performancebike.com/bikes...8_20000_400127

A lot of bang for the buck on the Ascent, and it does show temperature, so I'd strongly recommend it for your described specs.