Well the vanilla game for the price of 5 pounds, is a absolute bargain. The singleplayer without using any mods, is fairly simple(for me anyway) and can be enhanced with the use of mods, just remember that there is a cheat menu that can be turned on. In my first playthrough I used the cheatmenu to boost my money count a little bit.
Also there are hundreds of mods for the Mount and Blade Warband, each with hundreds of hours. Then there is mutiplayer which can be very addicting with its own mods, aaaaand when you have completed all of them or get bored, you can buy the DLCs which are all very good(except fire and sword), keep in mind though that Napleonic Wars DLC(most populated DLC) is multiplayer only.
Or you could buy the game including all the DLCs for just 17.00 pounds. (highly recommend getting this deal, as someone said before buy it twice).