Was there at an athletics event end august/start sept last for 4 days.
Very nice place but accomodation expensive. The day to day costs not a lot different from elsewhere in Spain, maybe 15% more as its the resort that well to do spaniards use for holidays themeslves. The Basque people nice, lots to see and do in whats a failry compact 'old town' area and my instinct at the time was that it was 'children friendly' and safe. Lovely beach and good cafes and bars etc. The shopping cente in the old town area is very cheap for food and drink stuff however. Lovely scenery, but not much english spoken - but you dont need spanish either.
Think you will enjoy!