Brisa Marina and Los Faroles on the main road opposite the beach (the non-pedestrianised part) both do excellent three course menu del dia for around 15 euros. I believe they are owned by the same family and have a lovely, friendly atmosphere - they are well used by locals which is always a good sign. These have a really good choice of set dishes - the fish is really fresh and particularly good - and I think one drink is also included (avoid the house wine, which is pretty horrid, and have a beer, would be my advice!) I think the MDD is available every day apart from Sunday.
Think Ca'n Josep also has a highly-recommended MDD but have never tried it.
Ca'n Ferra is also excellent and has been so for many years - we have been going there since 1995 and have never had a bad or expensive meal! Again the fish is really good and fresh (think they have a fishmongers next door).
Il Posito do fantastic MDD at lunchtime but are more expensive in the evenings.
The snack menu at
Stay is surprisingly cheap at lunchtime with lots of options for less than 10E. Fantastic setting!
One thing we have found when not opting for the MDD is that starters are particularly expensive - much more so than the UK, often costing at least 11E. For that reason we often go for dishes like paella or fish casserole, which are a meal in themselves, so a starter is not needed, especially if you fill up on bread and allioli first! Places serving tapas are usually good value too but can be indifferent in terms of quality.
If you visit the old town La Trencadora (an Italian restaurant) is really excellent value with main courses well under 10E.
I would agree that prices haven't really gone up in the last couple of years - in fact most MDD have stayed the same for longer than that. If you go to some other European countries now you soon realise that PP is, relatively, a bargain!