I recently started using WD40 to clean my strings, but my friend said that it would make them rust even faster and he said to use alcohol. What should I do, and I don't wanna buy some expensive fast fret.
The best thing would be to go buy string cleaner. I use Finger Ease and it works well.
Finger Ease. it's like 2.50 a can and works like god.

I put that on my strings and while it sits, I rub baby powder on the tips of my fingers. Ironic kind of, but damn I play fast.
Send this to you my master...
Here's to getting worse,
hope it kills you faster...
Show me how it hurts to rot from the inside out...
This vigil burns until the day our fires over take you,
Our father we forsake you.
I got some of the Dunlop 65 stuff today. It's pretty good, but my strings didn't really need it since I just got a new guitar, which had new strings on it already.

It made my acoustic's strings sound really nice though, almost like they were new.

And Fastfret's not that expensive is it? I thought it only cost $5 or something...
Saint Louis Blues
Neither, get Dunlop 65 or Finger Ease. Get something that is actually made for use on strings.