Honestly, I've never been to Eastern Europe, let alone in the Winter, but from what I've heard, it sounds like the kind of place I don't want to be at that time of year. I have a Ukrainian friend who lived in Odessa until he was 18 and can vouch for how unforgiving the cold can be in that part of the world. I'm with Knapp on Prague. By all accounts, it's a beautiful city and not as costly as it would be if you were visiting Western Europe.
As for Spain, you'll find it a rather diverse place and certain places will/won't be quite your cup of tea. I'm very partial towards Barcelona because it's home to me and it's quite nice there in the Winter time. Barcelona is more of a mixed bag if anything, but I love cities with eclectic character. The nearby Costa Brava is also fantastic. I also like the Basque country, you know, Bilbao and San Sebastian. Then, there's Mallorca and Ibiza if you want to go off the deep end. Madrid is nice, but it's every bit the proper capital city you'd expect it to be. Basically, the city is "what you see is what you get" and so are the people. Probably the best place to go if it's your first time in Spain.
I've been to Portugal, but it was for say two weeks when I was a wee tyke, and so I don't have the best recollections of Portugal. I remember having fond memories of Braga.
If you're really looking for a bargain, take KC's advice and visit Southeast Asia instead. I've never been to Asia (I'd absolutely love to), but I've always wanted to go to Thailand (for the beach resorts and the cheap shopping) and Singapore. My Filipino friends swear by the Philippines and with good reason. It's perhaps cheaper than Thailand/Singapore and while it's a drag to get from Point A to Point B, it's also a beautiful country that's really tourist-friendly. Also, most people there speak English as a second language, which really helps bridge the communication gap.