I found 10lb tanks filled for 45$ at the local fire supply place here.
Another place will ship 20lb tanks, aluminum for 90$(that's shipped cost!).

I think David Hui mentioned that a few days ago, I can see.

I get regs on line or from Victor, Victor make the best reg's in the business.
Cost more.........then I add a nupro valve and manifold it out to suit whatever distribution needs I might have.

So a tank, a valve, a regulator, some teflon tape, the gasket between the tank/reg, some decent tubing(Tygon is great IME, but silicone is also good), a diffuser/reactor, and you are set.

You will need to watch the rate and add more every so often.
I just watch the plants, if anything is squirrlely then I check the CO2.

A reg: 20$ on ebay
Valve: 15-25$
Tanks, 40-90$

I like the Aquaticmagic.com 's ADA beetle knock off diffusers.
They run 10-25$ and are about 4-5x cheaper and similar quality

Regards,
Tom Barr