This thread has some info for you: http://www.digitaldjtips.com/topic/portable-pa-advice-wanted/#post-2207821
Also, be prepared to sink serious money into a PA (as the OP in the other post is doing). If you are NOT willing to do that, the only sensible advice is to rent gear. You can rent fitting to each event, always have high end well kept gear, you can probably make 15-25 discount from the rental company and if something breaks down you can call them for quick replacement. Since either way you will have to customers pay for gear (at rental value, even if it’s yours!), financially it makes no difference for you bottom line.
Rental fees are usually around 4% of new value for big(ger) gear and to make buying and renting out a feasible venture from a business point of view, the consensus is that you should be able to earn your original investment back in 14 to max 16 months. At 4%, not calculating maintenance, storage (which you should), interest (even if you use your own money to buy, you lose the option of putting that money to work for you in another way to earn interest) and a few other bits and bobs, you will need 25 rentals in 14-16 months, somewhere between 1 1/2 and 2 times a month.
The other option on the table is to get yourself a decent (not top-end but close) backup set of two full range speakers (they will be strong enough for a 150 people party or even 200) that you can use for impromptu parties where there is no more time to arrange for rental gear, smaller parties and those parties you want to get for some reason, but are willing to “donate” the gear in order to get the gig. And rent for everything else.
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