http://www.nebulah.nl/?page_id=6

This guy will tell you how to make a midi in for your C64. I assume the c64 and C64c are pretty similar in hardware, just look a little different.

Tough to sync the 2600 unless you already have the Highly-Liquid midi adapter.
It will be impossible to buy anymore of these adapters from Highly-Liquid as I bought the last
6 today that John had and he is not restocking this item anymore.
He did hint that he might release the code and make it open source, but I don't know when.

Yeah, I was thinking that if it was too difficult or too expensive to sync them together, I would just have one of them be computer control and use midi controllers for the others. I already have an old Yamaha synth that I've been playing along with my game boy on, I just didn't know if there was a way to control them by computer.

using mssiah and MGB you will be able to control the c64 and the gameboy by midi~ these will be in sync. i don't know about the atari. maybe you can play that by hand while listening to the other two (REAL INSTRUMENTS)?

that'd be basically impossible to sync the three at once, seeing as the tempos wouldn't mix up right for any combination of the three. hn0, your best bet is to simply record them individually and sync them up (use Sony ACID, FL Studio, or if you can't really afford much i guess Audacity could do it).

c64 has weird tempos too, i dont know if MSSIAH also has these or if can slave to any tempo?

Its going to be hard to sync the 2600 because it can only produce the following tempos
224.71
179.77
149.81
128.41
112.36
99.87
89.88
81.72
74.90
69.14

PS - MSSIAH for c64 Midi, although I guess there are probably other options

You give the impression that you're pretty new to this sort of thing, so I would consider slowly building up this sort of complicated set up and thoroughly reseach everything needed.

****Wasn't sure what to put this under, so I figured I'd put it in here.****

I was wondering what would the best way would be to sync a DMG, a 2600, and a C64c together, if that is at all possible. I know synthcart for the 2600 accepts midi with an adapter, and I know that I can probably use LSDJ or mgb with a usb-link cable adapter or arduinoboy for the DMG, but I'm not sure about the C64c, so I wanted to ask what you guys think would be the best way to sync it all.
In short, what I would like to know is
1) If it is actually possible to sync all of them together(I assume it is, but I'm not sure as I have only limited experience with midi).
2) What software (for the DMG, 2600, and C64c), cables, adapters, and/or equipment would be the best to use for this(as well as whether I should sync them all with a computer or with the arduino, or if I'd need to run it through a computer).
3) If possible, the best place to get this stuff, as I'm horrible at finding good prices. Though this is mostly just me being lazy, so don't feel obligated.

Preferably this would all be on a budget of $200-250 (though this may be a ridiculous estimate, because, as I said, I have very little experience with midi and computer controlled instruments).

Thanks!