The wavy feeling is indeed a worn disc, i'm starting to get it on my rear disc as i think the pads i'm using are a bit harsh and i'm always on the back brake in traffic and it obviously does more work trying to pull the bike's weight with just the one caliper rather than 2 at the front.
When they say wavy they will mean grooving.
If it's a mild grooving then it's not an immediate issue, and it can buy you time to save a few quid but if it's really grooved then common sense says they need sorting.
You could get discs and pads for less than £300 though, but that would obviously mean fitting them yourself.
It's not a difficult job, but you need to take your time doing it so that it's done properly, making sure surfaces are nice and clean on the wheel hub, everything is torqued correctly, and while your at it clean up the pad pins and give the caliper pots a going over with a toothbrush and brake cleaner, then red rubber grease them up.
On a negative note, you've gotta hope you don't have any seized disc bolts, or you don't round off the allen heads of any bolt, 'cos that will stop you in your tracks unless you are equipped to deal with it.
Also, make sure you line up the lugs of the speedo sensor in your wheel when refitting, otherwise you'll snap them and be left with no speedo and another unwanted bill.
It's a common mistake, i've done it, as i'm sure many other foccers have too.
ps: make sure you thoroughly clean off the sticky residue from any new discs you might buy with brake cleaner.