2003 1.9 Gearbox failure - Bizz

Hi, My Ibiza 1.9 TDI Sport has a broken gearbox, I can only select reverse, 3rd and 6th. I had a 60k service some 700 miles ago and the car has been fine until Friday night when the gearbox went without warning. On the previous service the gear oil was topped up. My questions are: 1) has anyone else had this problem 2) Any ideas on cost, how long is a piece of string-type question I know! :-) 3) During the last service could the gearbox filler cap have been left off causing me to lose enough oil during the 700 miles for the box to fail and where would I look to find this?

Many thanks,
Bizz.