Towbar for 2003 320D

I need a tow bar for my 2003 320D, just for towing a trailer. I
have
been offered a Witter, but I am told that they need to cut the bumper
to
do this and I don't like the sound of it. What do I need to ask for
instead, or should I just get a BMW one? Funds are quite tight and
the
Witter one is quoted at £300, so expect that a BMW one will be at
least double.
Please help, or if you can fit BMW tow bars at a reasonable price,
please let me know. One to fit myself is not an option. Thanks.