If you look at the spacer between the bearings there should be a small notch on one end. You can use a drift/chisel/etc. to get on the inside of the bearing and drive it out of the wheel. Once one bearing is out, the spacer will fall out, and getting the other bearing out is easy.

Make sure and take out the speedo drive plate and the little ring that retains it before driving the left side bearing out (only applicable if your speedo is driven off the front wheel not the rear wheel).

The bearings are standard double-sealed type that should be available pretty cheap from any bearing shop... I paid about $7/bearing when I replaced mine.