I ended up ordering the Wahoo RPM Speed and Cadence sensor bundle rather than the other Wahoo BlueSC I linked to earlier because it was magnetless and also had a shoe mounting option for cadence. The cheapest computer I've found so far that should work with the sensors, were I to get a dedicated one rather than use a phone, might be the REI Garage CatEye Stealth EVO+. I'll post an update on how well just using a phone works once I get some time with the sensors.