You can offer your members to choose the amount paid for their membership themselves.
Allow members to modify the membership price
In order to fin this option, first choose "Membership Types" from the Members Application "Settings".
Select the type of membershipfrom the list and then select the "Rate" tab.
Then select the billing type, either floating date or fixed date.
For floating date memberships, check the box "Allow your members to modify the price". You will then be able to choose not to allow a price lower than the basic membership fee or set a minimum price.
Afterwards, when you purchase a membership, there will be a suggested price but the member will be able to modify it as they wish.