Of those options, the BBS one is probably the lowest cost, but -"shockingly"- that option is still available today... and is probably way easier for people to find your software than it was back in the day.
There are astroturfers out there who pretend that Steam is The Worst Thing Ever, but they distribute your game, dev-selected old (and pre-release) versions of your game, promotional materials for your game, and host forums and a news feed... forever. Valve also pretty clearly chooses to distribute games that are in the intersection of what's legal to distribute in the US and what the busybodies at MasterCard and Visa permit them to distribute.
If we lived in a just world, because of MasterCard's and Visa's enormous size, they'd be declared as something like "payment processors of last resort" and required to process transactions for anything that's legal to sell in the US, and subject to enormous fines if they so much as suggest to any merchant that MC/Visa will stop processing that merchant's payments for any reason other than a clear and obvious history of fraud.
Alas.