I don't have much more to offer over the other comments, other than to bolster the requests for more information. Would love to hear about what venue/service you're using for this, and if you're willing to share, how much money you're funneling into this kind of patronage. I'm very supportive of the idea of communities coming together to produce art in this way :)
Seems like it would put you in a position to publish a, say, quarterly collection of the results. Combine that with a Patreon or something similar if other people enjoy the stories that come from the prompts, and you might break even while still getting the stories you like :) Seems like most short story publishers run in a deficit so if you're accepting that from the start you're in a better position than most.
I'm actually contemplating doing this. I am a technical person with no time or energy on my hands to build shit in my personal time. So I'm putting together an RFQ for someone to build the site to automate a weekly writing competition with amazon gift cards for prizes. So I was thinking a semi-monthly issue of 8-10 of the top rated stories with royalties (if any sales) to the writers.
So I like to use a couple of ghost writers I have found on various freelancing sites (Upwork, elance, etc). Don't let their rates scare you away. Almost all of them work for fixed prices. I let them chose the price, then I add a bonus on top of that.
A story can cost anywhere from $50 for a 20 page novelette to $2500 for a full novel.
As a terrible writer, some times I provide my own short story, then work with a professional to plan out something bigger. I'm currently working on a 200-250 pager with a guy I found on upwork. This will cost me about $500 for the writing, $500 in bonus, $500 for proofing and editing, then I have a novel with full ownership - he will be on the byline if I ever decide to publish it.
