Will new operators always cost 25,000 renown?
Solution 1:
The base operators (FBI SWAT, GSG 9, Spetsnaz, GIGN, SAS), are the ones that cost 500 renown. However, that is only for the first one you buy for an operation team. (E.g. if you buy Ash first for SWAT, she'll cost 500, but the next will be 1000, 1500, and 2000 in whichever order you get them).
New operators (So far: JTF2, Seals, BOPE, SAT, GEO), are the ones that have been released per season in duos (E.g. Frost and Buck, Hibana and Echo) will cost 25,000 renown to purchase. Ubisoft has no intention of this number going down.
Their reasoning being that an average FPS player (including R6) will play 8-10 hours/week, which means it should take between 2-3 weeks to build up the renown and unlock the new operator. In total, about the length of a season and you should easily have both operators, and then the new season will roll out, with 2 new operators and you get to grind for them again.
Your other option is spending 600 credit (About $4 of real money) to immediately unlock one operator.
Your 3rd option is buying the season pass and unlocking all of the operators.
They want people to have the option to play for their operators, or to buy them, whichever you want. Either option is a win for Ubisoft.