I replaced both of my front wheel bearing assemblies on my 99 GLS 3.5. They'll cost you between $100-$180 for an aftermarket bearing assembly. (Autozone has Timken's for $124). One tool that you'll need is a Flange Axle Puller, which can be loaned out from Autozone ($20 deposit).
http://www1.autozone.com/servlet/UiB...e_axle_fwd.jsp
Just jack up the front end, remove wheel, brake calipher and rotor (I replaced my brake shoes and rotors at the same time). Disconnect the wire, (the part that makes the bearing so expensive) then attach the puller and remove the assembly. The new bearing goes on very tightly, I tapped my on with a dead blow hammer. Reconnect the wire, reinstall the rotor, brakes and wheel and your done. It took me an hour total for each bearing.