How to beat get cards for commander decks?

I know, I know the answer is to buy singles and websites like TCG player and such. My issue is that I'm a relatively new player started about 2 years ago and got a lot of precons but got into some hard financial times and had to sell most of them and now I'm trying to build some commander decks with the release of avatar and spiderman. My actually question would be is the best way to get cards that generally go in anything stuff like Sol Ring, arcane signet, ramp spells like Rampant growth,Kodama's reach and mana rocks in multiples? Like in the future should I get like 5 copies or just get the ones I need and move them around the decks that need them?