This year I've averaged about £30 a month in my tdi. I work away so it has periods of standing idle.
My mrs has a 1.9 tdi and a £70 fill up just about does her a month.
Plan is to give her my Golf and get myself an ED30 later in the year, as I don't do the miles anymore to justify having a diesel.
Although I have an A1 TFSI as a courtesy car and it's hard getting used to full tank estimates of about 275-300 miles!