Is the focus of the event on bringing people together or making money? If it's about reaching out to hard-to-engage parents and celebrating the school, charge less for activities and have plenty of low-outlay stalls to promote inclusivity. If the stall is part of a fundraising drive, consider charging more, but ensure that the cost is justified and have a variety of stalls so there's something for everyone.
How much does it cost to run? If it's a tin can alley, cans can be donated and bean bags borrowed, so the only cost is prizes. If it's a tombola with higher-value prizes it makes sense to price according to the value of the items. Refreshments stall prices should be dictated by the cost of the item on sale. Try not to skimp on things like burgers for the sake of profit - it's better to offer good quality and charge a little more than put visitors off with a cheap product.
Not everything has to be a set price - some stalls will have a price list that covers a range of items. When deciding on prices, consider the size, quality and appeal of each product. For example, the costs on your cake stall should depend on provenance - are they shop-bought, homemade by pupils or parents, or donated by a professional? A child's biscuits might be 20p, but a fancy decorated cupcake could be £1.50. Similarly, face-painting costs depend on the skill of the painter and the complexity of the design.
When deciding on pricing, be practical. It's easier to pay 20p or 50p rather than 30p or 60p as it only requires one coin. Try to limit the number of different prices at the event - for example, charge 50p per go or three for £1 for all games stalls. This makes it easier for volunteers, and parents know how much money to send the children off with.
When setting a price, try to avoid anything involving 5ps as they're small and fiddly for volunteers and nearly always require change.
Kids and adults
Bear in mind that there will always be more children than adults at school fairs, so it's wise to keep children's stalls cheaper as otherwise it quickly adds up for the parents. You can then charge more for food and drink for the adults.
Write it down
Include prices on a stall guide that can be laminated and given to the stall runners to prevent any confusion, especially if volunteers swap midway through the event.