RPi Alternatives for Self-hosting

Here is the thing, I have 4 RPi’s of different generations (all the way from Zero W to 4B 4GB) that I use to host services at home for personal use.

Lately, I have realized I am running out of RAM to host more services, not to mention not enough switch ports to connect to.

Now I know the obvious solution is to get a more powerful setup (maybe a thin client) but electricity isn’t cheap and I am not particularly in the best shape financially speaking to shell out $300+ on a decent client to host my services.

Any suggestions?