I'm sure you know this, but be careful not to listen too much. Studies have shown that people abhor losses. In fact, a loss of $1 is 2-3x as significant as a gain of $1 to them.
When a product first starts charging, it triggers that reaction. If you had described Mixergy to them and said "this will cost $5" some people would have probably said "sure I'd pay that". But those same people, when used to getting it for free, now feel a loss of $5 when the price comes in.
The point being, not only will they get over it in time, but your new customers (which you hope to be 100x the size of your current base) will never have felt that loss.
When a product first starts charging, it triggers that reaction. If you had described Mixergy to them and said "this will cost $5" some people would have probably said "sure I'd pay that". But those same people, when used to getting it for free, now feel a loss of $5 when the price comes in.
The point being, not only will they get over it in time, but your new customers (which you hope to be 100x the size of your current base) will never have felt that loss.