Montana has very good selection of cheap characters, just pass Mona and Avola to save money - they are great cards but not mandatory to make effective deck. Griezzo and Don are IMHO overpriced and you wont need them anyway.
Jungo has also range of great character at decent price. Zornado and Troompah are the most expensive characters you need to consider, but besides those two you can manage really good with below 3000 clintz characters.
Those two clans should give you really solid decks for 50k
Yeah,go Montana,they've served me well,i went about up to level 35 in this game with them,they've always helped me,plus it also helps if the clan has attack manipulation(it was for me,really developed my skills as a player in mono-situations)
Also good picks are Nightmare...few weeks ago they wouldn't be a real thought on this but with the Nightmare pack they've had,there's been an overload of supply,so you can pick them up on the cheap.
Then there's always the Frozn...small clan,but it's got a great bonus,and it's value is on the up-and-up.
Honorable mentions go to Rescue.