Hi Batbrit - here in Spain nothing is ever simple. The banks are an absolute nightmare to deal with and that is why many choose to go through an agent, as they will have more information about the way the particular bank behaves. You can go direct if you want to, but you will have to find every individual bank website and then try to deal with them, usually in Spanish.
I have sold several bank properties and some of the banks do tell their authorised agents what their minimum offer is, and that is not published on their websites. So an agent could be saving you time and hassle by letting you know that a particular offer is not acceptable. Often a bank will take a month or so to let you know their decision, by which time you may have missed out on something else.
As for prices, you can take that with a pinch of salt. I have dealt with a particular development for the past three or four years, where the banks have several properties. At one point they were willing to accept 40k but now their "special offer" is over 76k. They will negotiate a little on this, but their minimum is still way over the 40k. In my opinion they are wonderful houses which were originally 150k, but you would need to judge what is a good price for you in the current market.
My advice, for what it is worth, is to look at the price not in terms of a "special offer" but in terms of what you think it is worth. Do some digging, check out the area and what else is there and at what price. Come out and look and talk to the neighbours. Talk to agents and maybe you will find one you feel you can trust. Look at resales too, as they are often cheaper than the bank repos!
There are still a few real bargains left, but you do need to know what you are doing and you absolutely need a lawyer to check all the paperwork, as the banks really don´t check and don´t care either.
Happy hunting!