A dissenting view on making WP cheaper: if cheaper, there would be more of it. Too cheap, and one is a fool not to keep one's entire empire permanently in WP--only coming out when going to war. But who to war with when everyone is in WP? WP would become just a cost to play the game, which would be a pure econ game, no need for any weaponry whatsoever. Fun for some, but I suspect even many of the pure econ players enjoy the thrill of playing that game in a war zone.
WP has its uses, and the feature should be better tailored to those different purposes. One already gets over a full month of "vacation" WP per rl year, just for owning the country. Enough for many of us. For those who need more, maybe the accumulation rate should be greater than 1 for 10...maybe 2 for 10, 3 for 10..who cares, as long as countries are out of WP some significant portion the time.
For those with busy schedules--work, sleep, family, other hobbies, etc--blackouts would be ideal. I'd prefer to be in WP 20 hours a day. That still means 4 hours, more than I want to spend each day, when someone could war on me. 16 hours, even 8 hours a day would be a big improvement from the current 0 hours a day. For those who don't want to deal with wars during the work or school week, how about complete blackouts for 5 days of 7? I'd respect that.
With these avenues available, purchased WP should be made more expensive--a costly last resort, to be used sparingly.
What galls me to no end is seeing good strong empires, with good defenses, in WP for real-life months on end. Top 10 war rank countries, permanently in WP. Friends and foes alike (hypothetical foes, more like it)--I understand why one does it, and I don't mean any insult to those who do it, but I believe it takes away a key aspect of the game, when countries, especially in a war world, are placed beyond attack. Blackouts are the solution, and I haven't seen any strong arguments against them.