If you have 27 initial stacks out there then you are probably using 8,8,6,6. So you could continue giving rebuys with up to 8 more stacks of 8,8,6,6 and then you could just use 10 T1000 chips or even 2 T5000 chips. Later in the rebuy period I like to get the higher denominations out on the table. The players that rebuy can make change with the big stacks on the table. The more larger denominations you can get on the table, the less coloring up you will have to do later. You have have plenty T1000 chips to support lots of rebuys and still have plenty of chips to color up with.
How many players are you expecting? And how many rebuys do you think you will need?