I find the Balearics more expensive than mainland Spain for eating out and accommodation.
If you can bear flying as far as Malaga, which is under 3 hours as long as you're no further north than Leeds/Manchester etc, that opens up a lot of options, eg the aforementioned Torremolinos, also Benalmadena, Fuengirola etc.
Or in and around the city itself. Public transport in the area is good so you can travel around easily without needing a car as long as you're in walking distance of a population centre. Or a little inland is likely to be cheaper for accommodation and eating out.
Eg we stayed in Alhaurin de la Torre for a walking holiday and there were regular buses to Malaga, less frequently to a few other places or you could pick up the train that went up and down the coast. Young adults might like the massive outdoor shopping complex (Plaza Mayor) that had lots of Spanish and international brands, restaurants etc.
Or fly to Girona, Barcelona or Reus, lots of choice on the Costa Brava and Costa Dorada, you could have a day trip to Barcelona.
There's also things like water parks and Port Aventura the area which is an Alton Towers type place but I don't know anything about it because it's absolutely not my thing at all.