Upvote:-1
Your issue with customs has already been addressed so I would focus on the costs here. My credit card exchanges money at a rate specified by Visa or Mastercard and then adds 2.5%. In general that rate is some sort of central rate. If I exchange money for cash Euro today I would need to spend 4270 GBP to obtain 5000 EUR. If I exchanged the 5000 back straightaway I would receive 3676 GBP. Obviously you will not be changing it all back but I assume you are planning to have a contingency reserve and hope not to spend 5000. You can therefore see that although the bank charges seem high exchanging cash is not cost free either.
(Rates quoted above valid 26/02/2022 from the Post Office in the UK.)
Upvote:4
5000 EUR is under the limit at which you need to declare (10k EUR in Spain, 10k USD or its equivalent in many non-EU countries). For a developed country like Spain there is nothing to worry about here beyond whatever concern you'd normally have walking around with a bunch of cash.