The cost of a renewal is determined by what type of license you have. A Lifetime License does not have a renewal cost as it was configured to be a 1 PC license with no Expiration date. There is no renewal fee to maintain the license. If you purchased your Subscription License originally at the lower legacy pricing, then your renewal price will be grandfathered in and you will see no increase in your annual subscription rate.
If you purchased in August of 2014, you have an Annual 3 PC license for $24.95 a year (+local taxes). After the release of Malwarebytes 3 Premium, you are eligible for a free upgrade to Malwarebytes 3 Premium and your renewal will remain $24.95
If you purchased in October of 2015, then you will have at least a Single PC Annual License with a renewal of $24.95 a year (+local taxes). You also get the free upgrade to Malwarebytes 3 Premium and your renewal will remain as it is. If your license is configured for more computers than the price will be a little different but it will remain the same rate as you originally purchased for, excluding special pricing licenses.
The current price is $39.99 a year (+local taxes) for 1 computer. Again this license can be configured for more at an additional cost, and your renewal fee will be be the same as your purchase price.