Cheap wireless is unreliable as it's affected by stray emissions from all sorts of sources, including other nearby wireless devices and cell transmission towers. Reliable wireless is expensive. You also need more batteries: at least one in the readout unit and one in the pickup unit. I even once saw a totally absurd design that had 3 parts to it, EACH needing its own battery!

I have a wireless Sette FX-3, which mostly works OK but has several annoying features: Useless readouts like calories burned and fat calories burned, which are inaccurate and meaningless and just get in the way when you're cycling through the displays. The altimeter can't be zeroed out. It has auto-power-off but not auto-power-on; i.e., if it's idle for a while it'll turn off, but when you get rolling again, YOU have to remember to turn it on! Max speed all too often reads way high because I went past some cell tower. Other people report that their FX-3 is totally wonky out of the box, so their QA apparently sucks and I'm lucky to have gotten one that seems to mostly work correctly. If you can find it on sale for about $30 and want to take a chance, you might be lucky too. Oh, it doesn't have cadence.

Otherwise, the discontinued (wired) Ciclomaster CM-215A has altimeter (but no cadence, which I never found useful when I had it) and works well. I think there's some seller on eBay who has them at $15 or so.