I too suggest the Fluval Spec V. This 5G has three viewable sides and its almost entirely self contained, save for the power cords. At 5G, it's perfect for a betta and some smaller companions.
It costs roughly $100 but it is ready to go out of the box (everything but a heater - which depending on your ambient temperature you may not even need). Its stock LED will provide enough light for low-light plants (though just barely imo). I upgraded it to a Finnex Fugeray 16" which will certainly make your betta's colors pop (this was an additional $50 but not an absolutely necessary expense).