Can only really echo what others have said.
Round here (mansfield/notts) juveniles are 35-80 depending on colouration etc and adults are anywhere from £70-£300
"Standard" babies average around £40 round here in shops.
Check your local classifieds papers, we picked our beardies up at the equivalent of £25 per animal probably pence over after your include the bit of driving needed to collect them
Unfortunately there seems to be no such thing as "average" prices.
We are lucky enough to have around 5 reptile shops locally and prices vary wildly. As an example two shops here only about 15 miles have around (and over) a 100% price difference in some animals.