In my experience mobile contracts in Tenerife are much more expensive than in the UK. All mobile providers have their plans on their websites so you shouldn’t need to go in and ask until you’ve chosen the one you want. Besides Orange and Vodafone I suggest you check out Movistar, Mas Móvil, Hits, Lebara. I’m on Movistar fusion which bundles mobile, landline and internet into one service and one bill. I also made the decision a few years ago to just buy the phone I wanted and then choose a mobile plan, rather than being stuck with a plan that includes a premium to repay the phone long after the phone itself has been repaid.