Marcelo wants like 30 or 40 bucks, so I guess it depends where you go, but expect to pay 20 or more like ruecifur said.
Are yall serious? My friend went to extreme couture in LasVegas and paid 25 and got unlimited classes for a whole day.
$15-$30 is the average. You should buy a tee-shirt out of common courtesy if you are not asked to pay a mat fee (or the fee is waived/free).