What stakes do you play? How many players?
If you play a $0.05/.10 limit game with 5 people, that’s obviously going have different requirements than a $100/$200 no-limit game with 18 players.
For one table, you generally you want at least a full rack of your blinds (so if a $1/$2 game, you want at least a rack of $1’s)
Then you want a few racks (or ten) of the next two denominations, and then back to a rack or two of your higher denom chips.
Just as an example, if you were playing a $1/$2 no-limit game with your buddies, you might want something like:
100-200x $1
200-600x $5
200-600x $25
100-400x $100
100x $500
Again, this is just to give you a rough idea of what I was describing above.
With a $600 budget, you can get a rack of $1’s, two (maybe three) racks of $5’s, and two racks of $25’s from a closed/rebranded casino for around that. And obviously prices can vary greatly depending on condition, scarcity, quality, and composition of the chips. But this still should be a good start for you!
Personally I’d look for a casino that means something to me or for chips that I think look really cool, and then start to build a set that way.
You can put up a “Wanted” add or just keep your eyes on the classifieds.
Good luck and enjoy the journey!!