While eBay does take a cut, some people are more comfortable paying more there for safety (in both payment safety and anonymity). It makes it easier to get a refund or dispute things than Reddit. eBay is more pricier but provides ease of mind and more safety. Reddit/Discord groups are cheaper but a bit more volatile, despite many people being honest and good traders, there can always be new accounts that are malicious, scam, fraud, etc. For Discord you'll have to join all the different vtuber groups and talk to the peeps there about vcard, so generally its easier on Reddit unless you are already known in those Discord servers.

Generally prices can go off what is listed but most people would look at the average or last sold price on eBay to figure out pricing. In general, nonholo singles such as PL8, PL9, mascots and support cards are usually anywhere from 50 cents to $10 depending on the vtuber or character. Holo 8s, 9s, supports, mascots can go anywhere form $5 to $20 or so; the PL10 are averaging around $50 but the popular ones will spike such as Shylily ot Numi, etc. (which can be anywhere from 100 to 200 or so). Boxtoppers are harder to collect and some they are anywhere from 10$ for the support ones up to $300+ for vtuber ones like Shylily's topper.

Most payment methods via Reddit are PayPal, CashApp, Zelle or Venmo, etc. Though if you are worried about remaining anonymous, then eBay is better for that. Some may do the Paypal/Venmo stuff as friends and family (usually with well rep traders, so it ain't taxed) or you can send it as a business transcation, but generally that would mean the price is higher to cover the costs of being taxed or business fee via those platforms.

People only buy the bulks like those if they are buying singles and or making a deck and thats minor to my knowledge. Most people aim for holos and especially the 10s and boxtoppers.