I note you are looking for a cheap getaway and nothing wrong with that. Your best bet would be the Canary Islands where you should be guaranteed some sunshine for the week. However, if you are a sun "gambler" there is a good chance the south of Spain will be warmer, cheaper and better. That is if you book a holiday privately i.e. book accommodation, flights, transfers.
A 2 bedroom holiday apartment, centrally located with sea and mountain views in a decent resort will cost you around €200 for the week (you can get the same for around €650 per month in December/January). You are not guaranteed sunshine but the odds are 50/50 (even money). Flights will not be expensive that time of year.