You could make a shit load of money. But to estimate how much we'd need to know the area and just how non threatening you look. I've heard anecdotal stories of people making hundreds of pounds an hour begging (always very young teenagers).
Here's a few observations:
1. You'll also need an excuse not to go back to people's houses for dinner.
2. Church is not such a good place to target. These people aren't going to be carrying alot of cash and what they've got is for the collection plate.
3. Following on from point one and two your going to be offered alot of none financial help.
4. The money you make will decrease very quickly after the first few weeks. When people get wise.
5. Church goes aren't idiots, most will know they're being played. Their generosity may well be targeted at protecting the other more vulnerable church goes who will fall for your scam, and that might not work out do well for you.
6. This is probably illegal.
7. It's horribly cynical, and I strongly suggest you look for other sources of income.