Why not take a look a the IGPS products, the $150 you are already planning on spending could go towards a $90 IGPS50e in the US, it has everything you are looking for and the battery last way longer than your phone.

If you order them on eBay (betting the farm on getting a perfect device) you can get them for way cheaper out of China, shipping takes forever but way cheaper.

Then spend anywhere between $18 - $50 (again EBay out of China vs US) and get cadence sensor; speed sensor is over kill since the IGPS has built in GPS.

I'm sure there are other computers that would do the same stuff. I tried my phone and it just eats the battery alive running 4 radios at a time (GPS, Cell, BT, ANT+) and the display bright enough so you can see it in the day time.

Just a thought