In the truest sense, that is exactly what many people do. Maybe not for "$50," but for other things both tangible and intangible. The "selling price" is whatever takes their focus away from Christ and trusting in His will for their lives. Check out Matt. 16:25 -
"For whoever desires to save his life will lose it, but whoever loses his life for My sake will find it." (NKJV)
On the first take it may appear that Jesus is talking about one's physical life, but in reality he is talking in much broader sense. He is talking about who or what is in control of one's life. Or what is one's primary focus or goal in life. If it is one's focus to live only for the things of comfort and contentment that this world has to offer (wealth, material possessions, status among men, good times and partying, etc.), in essence, "saving" himself in his own eyes and according to his own pleasure, things will not go well for him in the afterlife. He will lose his soul, lose eternal life. In effect, he has "sold" his soul for whatever he lived for in life.
But if one trusts God, lives with the will to please him, places Jesus first in his life, in essence, losing or putting aside what might have been his own desires for his life, then that person will gain eternal life. One must sacrifice his own will and desires in order to live for Christ. This is not to say that he will or must live in poverty. God will see to his needs. "But seek first the kingdom of God and His righteousness, and all these things shall be added to you." Matt. 6:33
Following up with Matt.16:26, Jesus explains-
"For what profit is it to a man if he gains the whole world, and loses his own soul? Or what will a man give in exchange for his soul?"
This interpretation of these verses is further illustrated in a modern translation of the Gospels called "The Message." Matt. 16:24-26
"Then Jesus went to work on his disciples. "Anyone who intends to come with me has to let me lead. You're not in the driver's seat; I am. Don't run from suffering; embrace it. Follow me and I'll show you how. Self-help is no help at all. Self-sacrifice is the way, my way, to finding yourself, your true self. What kind of deal is it to get everything you want but lose yourself? What could you ever trade your soul for?"
So I would surmise that according to Jesus, it is indeed possible to "sell your soul."