I have installed VirtualMin GPL and found it very powerful.
When I wanted to upgrade to Pro version, I saw that its prices are a bit unusual.
I SUGGEST FOR YOURSELF, MR. CAMERON :
If you want to increase VirtualMin selling :
1- Add Monthly, Quarterly, Semi-Annually Payment Cycles
2- Remove the domain limitations. Instead add some different between dedicated server or VPS server prices.
3- Add more payment methods, such as libertyreserve.com
4- A more competitive prices with cPanel :
5- At least 15days free trial license.
The above features make it possible to test your product and choose it when see its power !