Bollocks!
You can get a return (well, two singles) for £40 Kings Cross to York. I refuse to beleive it'd cost you over £60 for a return to Kings Cross from Croyden!
Plus if you're under 26 (I think you are?) you can get a Young Persons Railcard for twenty quid which saves you 1/3rd of pretty much all train tickets you buy for the next year.