In Ebay, you can look here to see what people are ASKING for Russian postcards. If any of them looks like the ones you have, follow it until the auction is over (notice, I filtered out all but auctions). That will tell you what someone actually PAID for the thing (plus postage, hassle with Paypal, etc.) Then you can decide how to go with it. Ebay gets the biggest audience, but craigslist is free. ;-)