I've been offered £4 a kg for my wax from a candle maker, unrendered £3 a kg.
I don't know if there is a general 'going rate' but to me that sounds incredibly low.
I filter my wax into 1oz moulds from Thornes and sell them at £1 each. People buy them for making wax wraps, beard balms, etc. Also for waxing thread for doing embroidery.
1kg is 35 ounces. Surely even wax exchange for foundation would be a better option?