Can 2 different airport extremes modules be used together?

If you need more WiFi signal strength in the garage, then the garage is NOT the place to locate the extending AirPort.

Why? The signal quality is already poor in the garage. Adding an extender in the garage will only extend a poor quality signal, with little to no improvement.

Locate the extender about two-thirds to three-quarters the distance from your "main" AirPort to the garage. So, if it is 100 feet from the main router to the center of the garage, locate the extender at about 65-75 feet.

You should be able to find the 4th Gen AirPort for $20-30 or so on Ebay.

Yes,, but the speed is restricted to the max possible on the older airport.. which may not be particularly good..

Don't expect huge range improvements using those older products when the MC340LL (actually a Gen4 Airport and now 10years old) is probably pretty much end of life anyway.

I have been trying to find some online but there are so many not sure they all work with each other.

They do, if you are looking at the Gen 1-5 AirPort Extreme and Gen 1-2 AirPort Express.

The 2nd Gen Express is the latest version of that model.

What I really only needed was 2 more of those pucks to extend range out to one side of the house (kids rooms) and out into the garage.

Keep in mind that to extend the network, the AirPort must connect to the "main" AirPort on your network, not to another AirPort that might already be set up to extend the network.

So that would mean that the two AirPorts that you are looking at must both be closer to the "main" AirPort Extreme than they are to any other AirPort. If they are not, they will pick up the stronger signal from the closest AirPort, but they will not be able to extend the network if this is the case.........since Apple will only allow you to extend the network one time, not two.

Another way to say the same thing........any extending AirPort must connect to the "main" AirPort on your network, not to another AirPort. Here is how Apple explains this:

Important note

If another extended Wi-Fi base station ➋ is placed between the primary Wi-Fi base station ➊ and the extended Wi-Fi base station ➌, the extended Wi-Fi base station ➌ will not allow clients to join it. All extended Wi-Fi base stations must be in direct range of the primary Wi-Fi base station

if it were me then I would only purchase new airport devices to replace an existing installation rather than expanding, newer mesh wifi setup will support faster wifi speeds, while not having an apple logo or apple airport util support a new wifi setup will likely serve you better in the long run.