I don't find resistance kits expensive. You don't have to use them in every battle but against an opponent who you think beats you without your kit.
You can always buy some tokens (while supporting the game) and buy Premium Account. 2x IGC per match, it helps a lot if you use kits in every match.
I have spoken to most of the top players and I'm in the top 20 right now. We don't all use the highest resistance kit. In fact, I'm yet to meet one who does.
Here's your chance to meet a player who uses the best resistance kits in his game, it's me.
I don't do PvP battles for IGC but for ladder points. If i want IGC, i'll battle with NPCs. So, i can affoard to use the best kits out there.
Oh, i'm one of the top10 players.
Actually, in lvl30 area (where i fight), players either don't use resistance kits at all or when they do, it's the best kit. I've only seen 2 times when players used other than +25 resistance kit. One time someone used +16 kit and another one used +12 to all kit.
Since there are resistance drainer weapons in lvl30 range (-10 or -12 resistance drain per shot), using a resistance kit is basically a must, unless you want to be slaughtered.