I have 2 of these Wahoo bluetooth displays with a bunch of mounts so you can just pop it onto whatever bike you are riding.
https://www.amazon.com/Wahoo-RFLKT-Cadence-Bundle-Pack/dp/B00K8HVS60/ref=sr_1_1?ie=UTF8&qid=1510798132&sr=8-1&keywords=wahoo+rflkt+bike+computer
https://www.ebay.com/itm/Wahoo-RFLKT-BlueSC-Speed-and-Cadenance-Sensor/292284494389?hash=item440d837235:g:jJwAAOSw6HJZ2Q14
Yours for only $25.00
Also have an unlocked 64GB iPhone 6 which works great as a GPS computer with turn by turn alerts displayed on the Wahoo $300.