
Bike?! unless you have quite the limitations I'd try to keep walking or join a club and use their ellipticals than stoop to the bike level... I would recommend start resistance training exercises if you haven't already.. because you can either... a.) Baby the neck muscles, keep them the way they are, and have to work twice as hard on the bike... or b.) slowly begin to strengthen the neck/shoulder complex to help support your neck, so you can go about walking/jogging/etc...
As far as what brand to get for a bike... a bike is a bike... you just pay for the quality/features, so it depensd on how much you want to pitch out for a bike...