It's 500~1000+ bells plus whatever 8+ of the material is listed for the time period. Which is equvilent of doing 3~10 requests, or if you're lucky 1 rare big payout request.
Like any other mobile games, you need to ditch the deadweight friends if your friend list is either maxed out, or if they are just leeching off of you. If they aren't playing as much as you are, then you also need to remove them.
It's also good to get a mixed of players in different time zones, so you can find active players at different times of the day to see your request.
For me, my rule of thumb for any mobile game is if they haven't logged into the game for the past 30 days (same goes for FC on the 3DS), they are going to be deleted from my list to make room for active players.
There shouldn't be any reason when so many people are actively playing, that finding 5 random strangers to befriend AND assist in a quarry would take too long.
Right now I have 40 people on my Pocket Camp friend list. Of those 40, 32 of them have logged into the game within the past 24 hours. And of those 32, a little over half of them will respond to my quarry request within the 24 hour time period usually.
If you're having trouble finding Pocket Camp FC to add, there's plenty here;
http://www.belltreeforums.com/showthread.php?436574-Animal-Crossing-Pocket-Camp-Friend-ID-Sharing
You can even check reddit, twitter's #PocketCamp hashtag or twitch. It's flooded with new request every day.