I didn't have too much trouble doing it other than the engine dropping and scaring the hell out of me when I pulled the starter off...I even had the engine supported by a two ton jack but still managed to drop a bit..
The cost here is relative I think as if you put a cheap crank sensor on (£15-20) vs a better one for £50 then you might end up doing the job again really soon...
I know some engines you don't have to remove anything except the oil filter...(lucky them) mine was a AGG so had to remove engine mount, starter...and then got it off...
will take more than 30 minutes the first time you do it...and you can lube up the starter when you take it off if you have to remove it...

Everyone will need to do this job sooner or later....but you get to know your car better...

Makes me very reluctant to sell mine hearing all the horror stories about particulate filters and EGR valves...etc etc....
Stick with the golf...where else can you get used parts from other owners for cheap? Even new replacement parts are not really expensive...

Good luck in changing the crank sensor...then make sure your timing is right and most likely your car will be good to go!