Hi,
If the only thing you want is a lawyer to go with you at the moment of the purchase, I’m afraid I ca not help you, but relating the valuation of the property I can tell you that there are in Spain independent registered companies under the control of the Spanish Central Bank that can help you on it.
I don’t know whether under the rules of the forum I can give you some commercial names, but you can just write on google “sociedad de tasacion” and you will get some.
In case it does not work, do not hesitate to contact me again and I will give you some names.
Best regards,