Ah, good. You found the right place.
Firstly, it will depend on how much you have and what you want to keep. Even with the pound crashing against the euro, things are more expensive in Spain than UK including furniture, light fittings, kitchen equipment etc. White goods are now about the same as UK so it is pointless bringing them (they also take up a lot of room). Try searching on this thread and see if you can a few tips. I believe Digby Removals were being touted as good value and you may get away with a part load at fairly reasonable prices. IMO the choice in Spain is also a lot less that it is in UK, even if you want the IKEA stuff and put it all up yourself. Self hire vans can be very expensive when you take into account ferry and toll fares so look into that very carefully. Plus you have to budget for a return trip then getting yourself back. I did see a company (sorry, didn't get the name) where you can hire a van one way between UK and Spain and use it to drop off your goods. No idea of the prices, though.
A lot of people say they sold their stuff in UK and then bought new in Spain. When I checked into this, it would have been a very expensive way of doing it as the price for second hand furniture in UK is very cheap so there is no way you would get your money back and, if you have some good quality items you want to bring, the loss you would take would be more than covered by using a removal firm.
TVs are about the same in Spain now plus about 10%. The problem is, if you have a decent one you want to bring, you wouldn't get a good price in UK and would then have to start again so you'd be losing twice. Example, if you have an 800 quid plasma telly you'd be luck to get 200 on the second hand market thereby losing 600. Then you'd have to pay the 800 in Spain so you'd really be spending 600. The 100 quid it would cost on shipping would mean you'd only be paying that 100 extra, if you get my drift.
Good furniture in Spain is very expensive so think about that as well. An 8 quid frying pan in UK will be double that in Spain as are good quality pots and pans so bear that in mind as well.
Get a few quotes and look at the threads a little lower down. You should pick up some good hints and I am sure there are many personal things you don't want to leave behind so I reckon, when you take those into account, it won't be that much more expensive to add items of furniture as well. Beds, especially mattresses, do take up a lot of room on the furniture vans which may influence the cost and you can get those things from places like IKEA (not that I'd buy from IKEA, they all seem about 2 inches off the floor and I'd never get up again) . Our wood framed bed dismantles and we will be bringing that, just buying a new mattress in Spain to go with it.
Hope you find what you're looking for.