There’s a reason those accounts sell for upwards of $500
Best bet for most people is finding a plex server with access to these sites.
Once you have an invite, all you need is a computer with space and an internet connection. Download a bunch of popular new or older large freeleech torrents and seed for a month. For best outcomes, pay $10 for a seedbox and let it do it - usually faster bandwidth and less hassle.
Total time investment is 1-4 hours, + $10 for a seedbox if you want to accelerate/simplify things.
In those cases, anyone who wants an account is probably best off just having conversations and meeting new people on IRC/forums of some of these trackers. Both of those sites have a lot of active accounts, so with a bit of mingling, you'll befriend someone who can invite, plus you get to meet interesting characters along the way.
But yeah, I don't envy anyone actively trying to get an account on PTP/BTN. It takes a long time to build up the credits to invite someone, and more importantly, given things like tree bans when someone does some serious offense, you don't want to invite just any stranger.
I think that is the aspect I like the least about private trackers; as a whole, the scene can be a bit elitist and unwelcoming towards new users. I get that it is a difficult balance to maintain, though. On much less important forums, the ban evasion problems are already bad enough as it is, so I can't imagine moderating a place like PTP.