PA system for a huge Church with no budget!

I've been asked to spec out and install a PA system in 4 halls in a Church. There huge, not Westminster Cathedral but its the biggest church I've ever been in.

The main hall is 160 ft by 150 ft, the ceiling height is 180ft. Its a morbid damp stone building with fine acoustics for a bunch of choir boys I'm sure. Yet I've never done a church with echo for days.

They have no budget to speak of and want massive monoliths with drive units stacked to heaven. My plan is to install four (12 inch 4 ohm) drive units per side to just flood the place with sound from 40Hz/2.5Khz, maybe some horn drivers and strap a Cloud type PA amplifier to them. All made from 18mm ply. There will be no cross overs on the 12 inch drive units. I'll wire them into dual series and then parallel loads per side to maintain 4 ohms for the amplifiers. This must be as cheap as possible, I know they probably won't pay for all the hardware never mind my time and labor. This is a real charity case and a personal challenge for me.

Any suggestion on the best bang for the buck are welcome as I've never done PA systems on a shoe string budget.