It might seem a little steep to charge - however tees, balls and gloves probably comprise a fair whack of his base income - sale of bags, clubs, lessons, clothes etc are the upside - and where he can do his 'deals' for you. When I bought my two Vokey oil can finish SM4 wedges recently from our pro, he sold me them for £80 each - quite a nice discount on his ticket price (and today £95 each on Direct Golf UK). The shop will usually give me a pencil if I'm stuck :-)
I'm going to buy a new bag from him - Ping Hoofer. His price is £109 - so he beats the current price on Amazon by £1 (Amazon shows RRP as £135). I can hardly ask him for a further discount - and I won't. If I bought something else at the same time he might do a wee deal on the combined price - but that is up to him.
What you do get from you pro will be free advice and guidance - both on buying kit and on golf and the rules - and he gets to know you and if you have lessons he gets to know your game. So I'm happy to pay for my tees. But I take you point.