Well, what is cost effective for you?
There in Prague are many opportunities.
1) You can buy textbooks and learn by yourself,
2) or there are language school for foreigners (I'm not 100% sure, but I think some of them have got evening courses).
3) And there are many natives, who are fluent in english and teach czech for reasonable price (check internet).
4)And at least look for video lessons on youtube 