There is no free lunch. Tank purchases are a Catch-22. If you buy an old tank off of Ebay you then need to purchase a compressor to fill it. Otherwise, if you divide the remaining useful life of a used tank and add all of the hydro fees, visual inspection fees, and fill up fees from a 3rd. party vendor, you will see that your "bargain priced" Ebay tank is actually more expensive per year of useful life remaining than a new tank costs to operate on a yearly basis.
IMHO, the cheapest route for a newbie is to buy a new CE 6.8 or 9 liter tank and valve from Aliexpress and buy a Yong Heng compressor and aftermarket cyclone water separator for it to provide dry air. If you decide you love the sport, upgrade from the Yong Heng at a later date to a lightly used dive compressor from Craigslist, Ebay, or the AGN classifieds. if you are truly hooked, buy a new Alkin W31. If you are a trust fund baby, doctor, or hedge fund manager, buy a new Bauer.
The under $2,000 utterly dependable compressor has yet to be invented. A few guys get lucky and have one that lasts but they are the exception, not the rule.