Don't cheap out, since cheap cyclocomputers can have various issues, mostly with reading false double counts from reed sensor or from radio interference.
Long time ago, I had a cheap cyclocomputer that was wired and used the normal magnet and reed sensor system to read speed. Unfortunately, there was something wrong in the reed sensor and occasionally it read "double counts". The computer apparently wasn't smart enough and thus occasionally gave false maximum speed readings. A brand name cyclocomputer would probably not do this. Also, it was very sensitive to placement of the reed sensor. If it was slightly misplaced, the "double count" problem was continuous, i.e. I all the time got twice the amount of speed and twice the amount of distance. However, a perfect placement would eliminate this problem only 99.99% of the time, i.e. distance would be accurate but the 0.01% time problem would give false maximum speed.
Then, that computer broke after the bike had been several years in storage. I tried to find a good replacement and bought another cheap cyclocomputer, this time wireless. It too gave false maximum speed readings. I found I had to mount the computer and the wireless reed sensor on the same side of the handlebar to slightly improve the wireless connection. This time, the false maximum speed readings got rarer, but then I once noticed when I went to a shop, parked the bike before going to the shop, the maximum speed reading made sense, then after being at the shop, the maximum speed reading was false! So apparently the bike read counts from the wireless sensor while stationary, probably reading radio interference as counts.
Sigma BC 5.0 WR would be about the most basic reliable brand name bike computer you can find. It's wired, not wireless. It has one button, though, but that probably is not a negative feature.