OP, I started a children's consignment sale for our church last summer. We just had our 3rd (and most successful) sale yet!
To get the first sale off and running with a minimum of $$, we had to do a few things...
-Ask sellers to provide a rack for the sale. We also required all sellers that first sale to work.
-Offer a higher percentage to encourage people to sell with us (we give 80%, whereas most sales in the area give only 70%)
-Borrow, borrow, borrow! We borrowed the adding machines, cash boxes, rubbermaid bins, etc.
-Luckily for us, because we are a church ministry we had free use of our Fellowship Hall, plus all the tables and chairs. So luckily we had no expenses there.
-Homemade signs -- we bought some posterboard, made huge copies at Kinkos, pasted them to the posterboard, covered them in contact paper and affixed them to wooden stakes.
-Keep it small!!!! It can be overwhelming to have too many consignors, IMO. There are some sales around here with upwards of 1000 consignors. I can't even imagine trying to coordinate something like that. Not to mention I truly believe the quality of the items suffer. We had 29 consignors for our first sale, this fall we had 54. I think we will max out at 60. A) We don't have the space for more than that. And B) we already have a reputation of offering items in excellent condition, and I think a lot of that is because with so few consignors we can really control what goes in the sale. We also are a 1-day only sale.
Any other questions, just ask. Now that we just finished out 3rd sale we have had the money to build/purchase our own racks, adding machines, cash boxes, professional signs, etc. It has been a very profitable fundraiser for our mother's ministry and I have really enjoyed being in charge of it.