If you have a bass and no amp, get an amp. A cheap bass with good strings and a proper setup will be fine to start with.
If you are going to be playing in a band with a drummer, I doubt a 25W combo will be loud enough. Consider putting the money for the new bass towards a better amp instead. There are many variables and choices to consider, and many threads on suitable setups for beginners on TB, so before you start looking at wattages and brands, I recommend determining your needs and finding a solution that meets them. Its just as concerning seeing a guy hauling 1000W and 4 cabs worth of sound to a bar gig as it is seeing him walk in with a 25W practice combo
