SmartPropoPlus is Free and will stay so. You can always download the program from SourceForge free hosting.
SmartPropoPlus is an Open Source project. You You can always download the code from GitHub free hosting.
However, the hosting of this web site that includes a Forum and much documentation cannot be free anymore. The cost of a reasonable web site hosting is $60-$100 annually. A small $5-$15 donation will help moving the site to such a hosting sever and maintain it there.