To sell the rights to something, you first have to have rights to sell. Have you filed formal government paperwork to register copyright and trademark for your game? If not, you probably still have some automatic copyright protection in most countries, but it will be a lot more difficult to sell. If you can't afford advertising or a $100 fee on Steam, you may not be able to afford to file the paperwork for registering copyright/trademark.
Next, you have to find a buyer who is interested in purchasing the rights and sees a potential for profit from the purchase. There's no guarantee that anyone will want to buy the rights to your game. Most indie games are not exceptional and would have a hard time finding a buyer. There can also be underlying issues, such as poor-quality code or badly organized files, that affect the value proposition.
I think a good general rule of thumb is, if you have to go looking for a buyer, you probably can't expect much of a payout. If a potential buyer contacts you on their own initiative, that shows they are very interested in the game and see a lot of profit potential; then they're more likely to pay you something worthwhile. However, this is extremely unlikely to happen unless you have had enough success for word of your game to spread around. This takes you back around to the advertising problem - you need to advertise your game so it has more players so that you can show that the rights to the game are worth buying.
Third, you'll need a lawyer to help you with the selling process. If you try to go into a potential sale without a lawyer, the buyer is going to run you through the wringer and you'll be lucky to walk away from the deal with pocket change. However, if you can't afford advertising or a $100 fee, you probably can't afford a lawyer (unless they're willing to work on commission, which they won't be unless they see actual profit potential out of working with you).
If you have a formal business (with employees/salaries/revenue), you might consider asking your bank for a business loan to use for marketing. Otherwise, your best bet is to try to market your game on forums and social media (e.g. create a Twitter account, Instagram account, and Facebook page, and post regularly about the game).
If your game has a low score on Steam, you're probably already sunk. Nobody is going to want to buy the game on Steam or buy the rights to the game from you if the game has a bad score. Your best avenue would be to release some updates that address complaints that players have about the game, and put it on mega sale to try to draw in some new players who are willing to try out a game with a low score if it's very cheap.
