I firmly believe that within a set price range (especially for speaker on stick shows) that the resultant sound is about 20% the specific speaker, 40% the interaction of the speaker and the room, and 40% the skill of the operator.
I would highly recommend renting for your first ten shows and trying a variety of boxes rather than running out to buy the only thing available in your area. After you have enough shows to have your own opinions about what you need, than it is worth going shopping.
I would add to this by saying that renting will not only help you find what works for you while you learn how to make it work, but it will also give you a taste of the "real world" of managing expenses in a small business. Remember that many of the people who are advising you for free are small business folk. Taking that advice and copping the "I'm just an amateur having fun" plea is not going to make you popular with the other serious sound folk in your area. If you're going to provide a service....no matter how well meaning....make sure it pays for itself plus enough so that you cannot be accused of being a terminal low-baller.
People make their livings doing this. Don't foul them up.
