Difficult to quote future pricing and version changes - what it has been up to now is:
Educational upgrades (assuming you are still a student) are about half the cost of the already discounted full versions - in the US/Europe that means 95 instead of 195.
Version change time varies - it has been longer in the past, but I think there is an effort to shorten the time somewhat - but it is not a new version every year. Figure between 2-3 years, tending towards 3.
Don’t forget that old versions do not expire, so upgrades are optional, and that older edu versions are still valid for a commercial upgrade once you are out of school at the next version change.