Like Heitzso reported, I've successfully used a tally sheet broken into range values to manage statistics on a sliding scale admission scheme in the past (hint: make the most common expected price band amounts have the larger tally area). I've moved on from that since.
For my weekly dance I didn't want to administer the complication of a true sliding scale, yet wanted to try a similar concept to see how our community might engage with our revenue issues. As a result we've gone to a "You Pick A Price" scheme, described here:
http://mondaycontras.com/pages/you-pick-admission.php .
This has worked out extremely well, with self-selected admission payments greatly skewed towards mid and higher amounts. Very few pay the least stated amount or lower and several give us additional donations on top. The net effect is we have been able to pay each of our performers something on the order of $10-20 or more on average vs. our prior standard admission scheme (while still enabling financially challenged folks to participate if they can't volunteer).
I set up a cheap Android tablet with the Square POS (Point of Sale) app on it to manage the admissions scheme. After a short initial training period our door sitter volunteers have come to praise it and can process in dancers quite quickly. You can see our "process manual" here:
http://mondaycontras.com/pages/volunteering/door-sitting-process.php . The Square app itself is free and cash transactions incur no charge - credit card transactions do pay a fee (we only offer cash sales publicly). The reporting is quite good and you can manage cash drawers and see sales reports by item.
Should you decide to go with Square and find the information I've supplied to be helpful, I'd appreciate you signing up via one of the referral links from the groups I'm working with (you and the selected group will each get free credit card processing for 180 days/first $1000 of sales as a result):
Note: you must sign up by clicking on one of these links to obtain the credit. There is no way to gain the credit if you sign up in their standard way starting at their regular web site or via the link included in a retail reader package. They are very firm on this.
You do need at least Square's basic mag stripe reader to set up the app for the first time. However, they will send one for free upon request after sign up or will rebate $10 to cover a retail purchase (units available at Staples, etc.).
Please give me a shout with any questions,
Don