I would recommend saving up for a decent one. I have found that with cheap computers, you end up upgrading anyways, wasting more money.

I'm very happy with my Wahoo Elemnt Bolt, I just use the GPS speed, not the speed/cadence sensor, my Stages power meter also provides cadence readout.

I havne't tried their heart rate monitor yet, but I think it is reasonably priced at $50, I'll be buying one of those to try out in a few weeks.