IMO there’s little need to buy new in the computer world unless you want to do something silly like have a snapdragon x laptop or have the disposable funds to go the gaming rig route.
My desktop is a retired business workstation, a HP Z420. I bought it for $250, installed a smaller SSD ($100 new) for the OS + apps, upgeaded to the “best” Xenon that fit the socket ($150 used), upgraded to 64 GB RAM ($107 used, yay ECC memory being dirt cheap on the used market), and a 1070TI ($225 used, purchased just before covid).
It’s more than fast enough for my needs still.
This was all about 4-5 years ago, so you could probably do even better with more modern hardware.
It will decompose, but only it a hot compost pile.
To some extent, this means large scale composting, but you could theoretically do it at home if you live somewhere with four seasons (specifically fall) and have trees that drop leaves on your property or nearby. Let your grass get a bit taller as the trees start turning and mulch/bag the grass and leaf mixture. Bonus points if you have a ratio of 30 carbon (brown stuff) to 1 nitrogen (green stuff) by weight. “Normal” composting into. This is why big piles of fresh mulch get pretty warm and stream in the middle.
I don’t know what it would take to break down PLA in compost, but suspect it would take more time than a typical home pile if you manage to get it hot. It would probably be benefit from shredding to speed things up, as would the rest of the stuff in a typical compost pile. Amusingly, your PLA is probably ripe for getting whacked with a hammer, or a hammer mill.