Me and my partner want to visit Spain for a week on a budget for 400-600 euros per person but we are unsure how to do it as cheapskates.

We can leave from either NL (Amsterdam/Eindhoven airport) or UK (Manchester airport). We've noticed flights to Benidorm are some of the cheapest to Spain likely due to the excessive tourism there, is it the cheapest option? We just wanna have a chill vacation and mainly swim/eat.