Sure you can. The first cage/squat rack I bought, (I have two now for convenience) they couldn’t give the damn thing away. It was $600 new and I bought it for $150. A $500 recumbent bike from the same place cost $100 brand new. I bought a new set of Powerblocks for ~$400.
Everything else I bought used.
I have a functional trainer/”complete” home gym machine (Inspire M4) that retailed for about $4k IIRC. I picked it up for $1600.
That takes care of anything I want to do with cables, as well as taking the place of the barbell for a lot of exercises if I so choose. One of my cages also has a cable pull, which gets used quite a bit as well.
Bars, weight plates, etc can be grabbed on FB Marketplace...before and after Covid, prices were pretty reasonable. I have more olympic bars than I could ever use...I think I paid like $150 for 5 of them and around 200lbs of plates back in 2019. I have hundreds of pounds of both olympic and standard weights. I paid very little for any of them.
Any type of cardio machine can be had for a song by just watching Goodwill.
I love my gym and I use it every day.
I never heard of Facebook Marketplace. I know when I went online during COVID, I could hardly find anything, and what I did find was way overpriced.
When the rush at work is over, I may look into this.