I have about $600 and would like to know the best graphics card I can find for that money
If you have just 100 dollars more you can get a pretty decent used Rtx 3090 and with the money you have you can get a Rtx 3080 I think which is the second best card of the series 3000 (not counting the 3080 ti which came later and is in the same league as 3090).If you are asking for mining 3090 and also 3080 are great cards too,the only problem is that now we are in that crypto winter or bear market as everybody else calls it and the profits are not that good.
With just one such card in your home PC if your PSU accepts it,you can try mining before venturing further,you can keep the card to play games and do other activities during the day and try mining at night,you would get an idea.With that money though,3080 is the best option or you can buy 2 x Rtx 2080 ti which gives you the same hash rate as the 3090.Lots of choices now that the prices of video cards are down.
