A lot of the expats I know use a solicitor to do their Spanish Tax Return.  I'm amazed at the fees the solicitors charge them.  In some cases this can be hundreds of euros, and is often more than the actual tax that has to be paid.

In fact, I bet the solicitors don't even do the tax returns themselves.  They will probably get an asesor/gestor to do it for a fraction of the cost and the solicitor will pocket a nice margin on the deal.

I know you could try and do your own tax return, thus paying no fees but I wouldn't recommend it.  Spanish Tax can be an absolute minefield and there have been a lot of changes over tha last couple of years in relation to what deductions can be claimed for example.

You can actually get a appointment at your local tax office and they will submit your tax return for free.  However, it can be difficult to get an appointment as they seem to go as soon as they're released.  Also, it's not really in their interest to try and reduce your tax bill.

The best option, in my opinion, is to get an asesor/gestor to do your tax return.  You should expect to pay around 40 to 50 euros for this.  My asesor charges 40 euros if we do a joint tax return, or 50 euros if we need to do them separately.  He calculates whether a joint or single tax return is the cheapest.  All I do is turn up with my borrador and the various documentation needed and hand them over.  He then calls me a week or so later to say everything is ready to submit.  I pop back in, check it looks ok, then he submits it to Hacienda.

Using an asesor/gestor is the approach that most of the Spaniards I know take.  It's a cheap and stress free way of getting your tax return.  Solicitors should definitely be avoided.