If you don't want to read a long explanation, bottom line, for 25¢/50¢ blinds, 8-handed, assuming a $50 buyin, you can generally get by with:
25c x 100
$1 x 160
$5 x 220
$25 x 20
That's a 500-chip set. Similar to
@xdan's recommendation.
For a TL;DR explanation of where these numbers come from, and considerations for adjusting those numbers, read on.
The truth is, it really depends on how your game plays, but you want to start with buyins. I'm assuming $50 (100xBB).
Starting Stack for each person could be
12 x 25¢
12 x $1
7 x $5
8 handed, you'd need
25¢: 8 x 12 = 96, rounded up to 100
$1: 8 x 12 = 96, rounded up to 100
$5: 8 x 7 = 56, rounded up to 60
For your game, you need to decide what your workhorse chip is based on how your game plays and how your players bet. You want to get more of those chips in play at rebuy time. You don't want to give out another starting stack for a rebuy, because the number of chips (especially fracs) will quickly reach ridiculous levels. Just give larger chips on rebuy and let the player make change at the table. This generally comes from the person that just busted him, but it may come from a couple people.
If your game plays bigger, do you rebuys in $5 chips. If your game plays smaller, do your rebuys in a mixture of $1s and $5s (like 20x$1 + 6x$5). How many rebuys do you expect? 4? 6? 2 or 3 per person (so 20)? Add on chips to account for those rebuys. You may want to get the first half-table of rebuys with your workhorse chips, then go right into 2x$25 after that so chip stacks don't get too crazy.
So your rebuys might look like:
$1: 20 x 4 = 80
$5: 6 x 4 = 24
$25: 2 x 16 = 32 (I probably round down to 20 here, but it's gonna depend on your group)
Or
$5: 10 x 4 = 40
$25: 2 x 16 = 32, rounded down to 20
I have a feeling that the $1's and $5's in this sale will be readily available if you want to add on later, but there's no guarantee. Consider future-proofing this set to accommodate your game growing to 10 players.
And if you're still reading, some people like deeper starting stacks, like
20 x 25¢
20 x $1
5 x $5
That will result in needing more chips just for starting stacks (still need to add your rebuys).
25¢: 20 x 8 = 160
$1: 20 x 8 = 160
$5: 5 x 8 = 40
While that will mean more chips (and cost), it will also mean a bit of future-proofing built in (because you can reduce the starting stack to accommodate more players).
A good cash set for 25¢/50¢ that can handle $100 buyins, up to 10 players, with plenty of rebuys would be:
25¢: 120
$1: 200
$5: 240
$25: 20
Add it up. That's 580 chips... Can't have that. That last barrel is either 5 extra chips of each denom (for the eventual misplaced/lost chip), or add a barrel of hundos (or 10 more $25s and 10 hundos) and know you'll never run out of bank.
