The MOTU 24I has 24 inputs, but it only has TWO outputs.
If you want 24 full I/O for your studio at the lowest price, here is a suggestion:
Core
MOTU 2408mk2 = $900
Alesis AI3 $400 X 2 = $800
Total = $1700
If you go this route, make sure that you do not get the old 2408 because it is unbalanced using RCA connectors. The mk2 version has balanced TRS I/O. You can connect the two AI3 units to two of the lightpipe sets and use the MOTU unit as your PC interface. I have the old MOTU 2408 and I am using one AI3 with it, and it works great.
If you have some cash and want more LEDs on your modules then you can buy three 1224 modules:
Core
MOTU 1224 = $1200
Expansion MOTU 1224 $900 X 2 = $1800
Total $3000
At that price you might want to spend a little more and get
the Tascam MX-2424 for $3600.
But really, you can go with one of the MOTU options and buy one piece at a time and add more units as you get the money. Of course, you will need to get one of the core systems first.