I do think that monitors will play adequately loud. I say that, having owned a set of Monitor Ones. I'm an audiophile, with some
very expensive equipment, and those Monitor Ones impressed me. Incredibly good sounding speakers, and that's not even making
allowances for the fact that they're so small and (by my standards) inexpensive.
I wouldn't argue with anything written here, it's the OP's desired application that I question.
I used to jam along to tracks at a reasonable volume using a pair of Tannoy monitors. They sounded awesome. With near-field monitors, however, you really need to listen up close to realize their benefit. Sure, maybe they seem loud from a distance, but try using them with a hard-hitting drummer or half stack cranked to 11. If your live instruments are very loud, your studio monitors will not keep up. They are not designed to keep up.
A powered PA speaker has a couple of advantages over the studio monitors
for this particular application. A larger woofer allows for louder bass without causing the speaker to jump out it's enclosure. A horn-loaded high frequency driver helps to efficiently project and disperse the highs. In other words, it is designed to be heard in a room with live musicians. Furthermore, a powered speaker can sit on the floor like a monitor wedge, or mount on a pole, allowing the user to easily place it in the best location. The benefits of correct speaker placement in a live setting cannot be understated.
I'm only trying to read the OP's request. He seems to want it cheap and loud. Forget setting up a receiver or amp, running speaker wire, etc. Get one Behringer powered speaker (less than $200), plug it into a wall outlet, point it at your melon and GO!!!