I have no clue about "cheap" service providers. When I used "shared hosting", I did use Pangea ( https://pangea.org ), which is not the cheapest but it's promoting ethical and solidarity hosting, which helps/supports many ngo's, etc. and is Based in Barcelona, with good infraestructure, etc.
Something similar, for ngo's and social movements, is provided by nodo50: http://nodo50.org/ , probably based in Madrid.
Another approach is to hire your own virtual server, and then, you get there as many tikis as you like (you do your own setup of the apache, mysql, php, servers, there are useful guides in the internet). And some of us use ISPConfig as a free/open source control panel to help us manage the whole server, create websites, etc.
Most of the virtual servers I co-administrate are in Dimensis, which is a company based in Tarragona (also supporting communities using community currencies, and more sustainable local economies, etc., but you can pay them in euros, of course, also: http://dimensis.com ).
I hope this helps!
Cheers, and welcome to the Tiki Community!
P.S: btw, did you know that there is a Spanish forum also ;-) :