Grinding sound from rear wheel I am getting a grinding noise from the rear wheel which has got louder and is causing increasing resistance over the last few weeks (I live in the Netherlands so cycle every day). 

The cassette has been taken apart and cleaned in case it was dirt between cogs, this didn't help. From this I am guessing it is bearings? I've been told that if I took it to a bike shop they would just replace the rear wheel which would be very expensive. Was hoping that maybe the bearings could be changed or that its a different problem? 

My bike is a Scott Mountain bike with 21 gears. 

Thanks so much, any advice would be really welcome as I am a student with little money :(.
Thanks, James
There are two main types of cycle wheel, cup and cone and cartridge bearing.  Cup and cone bearings are fairly easy to service yourself with some simple tools, normal and cup and cone spanners and some grease. Cartridge bearing hubs need more specialist tools, presses to install and drifts to knock the old bearings out.

You can tell which sort you have by looking at the axle, if it's got a nut and a thin lock nut then it's probably cup and cone, google some pictures to see what they look like.

If it is cup and cone then taking it apart (only undo 1 side btw or you'll lose the centre of the axle), cleaning the loose ball bearings you'll find under the cones, then regrease and reassemble may sort the problem; however if its actually as bad as you sugest the ball bearings may need replaced and if the races that the ball bearings sit on are pitted then the wheel may be beyond help. There are lots of videos on the web showing this process.

If it's a cartridge bearing hub then your local shop might be the way to go unless you want to invest in some tools.