My wife and I used Jean-Paul at Sunflower in Benijofar:
https://www.sunflowercostablanca.com/They charge Eu 60 per person - this included an initial meeting to tell us what documents we needed to get together, making the appointment (at Orihuela, rather than Torrevieja, because it's a lot less painful!), meeting the week before to check our documentation and make copies as required, paying the required fee at the bank, driving us to Orihuela on the day of the appointment and translating. On the day, we were in and out of the appointment in 15 minutes.
Some people will tell you that you can do it yourself, but we'd tried previously at Torrevieja and although our solicitor had made the appointment for us and completed the application forms, they wouldn't entertain us without a translator. The translators I contacted wanted a minimum of Eu 50, so we thought it was worth paying extra to Sunflower to make the process as simple and pain-free as possible.