Evolution question

Hey guys, I was wondering how to handle a specific evolution. I raided myself a 98% wheaterboosted Porygon a while ago. I plan on evolving it to Porygon-Z once Gen 4 is in the game. But I was wondering: should I evolve my Porygon already (currently walking as buddy to get the required amount of candy, I haven‘t got that much) and later on P2 to P-Z, or wait until Gen 4‘s out? Do you think P to P2 could cost only 25 candy once P-Z‘s available? I don‘t know how it was handled with Horsea, when Gen 2 and Kingdra came out.