Yes the Goodwood shop is pretty pricey for overalls.
I got mine on eBay for £12.50 + £4.00 first class postage. The seller I bought them from was Workwear & Industrial Warehouse
, who appear to be closed until the end of the month, but there should be plenty of other sellers out there.
On white overalls you can scan or download badges, print them on transfer paper and then iron them on. It doesn't work for coloured material though, so my son's badges were also bought on eBay.