While the Teach Yourself Welsh course is good and useful, it focuses too much on the Southern dialect and a more...shall I say "Welsh" class style of Welsh? By which I mean, think of English class at school, and the grinding in of proper grammar. While useful and interesting, it won't help too much if you want to know how people really speak in Cymru. The Colloquial Welsh course is different, as it teaches about both dialects, and gives the language as used. However, I've heard that the audio tapes aren't as well-polished as in Teach Yourself. It really goes more for what you're gearing yourself towards.
And as for a cheap Welsh-English dictionary, I can think of nothing cheaper than the internet, with geiriadur.net being quite fine, though not having definitions for all words. http://www.cs.cf.ac.uk/fun/welsh/
is an online Welsh course, with a more complete lexicon (in my experience).
Hope I've helped at least a little!