Do you mean that you are tall and require a longer than standard putter? If so, putters come with different lengths of shafts and as long as one of these is suitable it shouldn't cost more than standard.
Simple really. If they don't have the right length, get them to +/- the shaft for you. If it's an expensive putter, they might not charge you. If it's a £50 putter, expect to pay for a new grip (£8-10).....
I had mine cut down from 35 to 34 and knocked upright. As it was already MY putter, I paid for the grip.
It's not your height that is the important measurement, it is the distance between your wrist (whilst stood upright with your hands down your side) and the floor. Have a look at the Ping WebFit for putters on the main Ping website - this will explain it all. If in doubt, ask your Pro.
getting it cut down shouldn't cost anything, they can remove and replace a grip with no damage as was done with my Karsten grip.
getting one extended beyond standard length might cost you, (around £3 - £5 at DG) but again needn't require a new grip if they know what they are doing.
Go somewhere reputable and get them to look at your address position before doing anything. Everyone has a different way of putting so make sure you get it checked holding and adressing it as you would on course.