Honestly i'd say era has the most longevity of any of the servers. I will say that for a new player starting off who plans not to spend any money then yea era might get a bit boring, but for me, yea I spent some money to get some guns when I first started, and 5 years later i'm still on the server.
I don't consider it a waste when it has given me this much enjoyment, more so than spending say $100 on a console game that is fun for a few months to a year.
The only inapp purchases I have ever regretted was back before era came out and I spent a bunch of money on furniture on classic which I ended up selling for half price to buy some hat because back then I thought it was cool to have lots of different hats even though I only wore 2-5.
Either earn 50k or spend $20 and buy the default rifle or the m4, and you will have a solid enough gun to allow you to compete against the more expensive guns and stop you from getting bored for several months to a year.
(Just saying, whilst yes the guns on era are very expensive, and other servers like classic bash era for the prices, at least the things you buy you can actually use, the majority of classic has probably spent more money on hats, furniture, morphs, 200k mounts than most of eras gun store weapons combined. How do I know this? Just look at the classic thread showing off hat collections, you don't get 30 4x8 hat pages for free, and classic hats are not cheap either)