My retaining was on my home is collapsing from the rotting railroad ties. I just purchased the home in February and it is my first house. I am only 22 and work full time as well as go to school so I do not have the money to spend on replacing it. Is there a cheap way to hold it off for the time being? It is around the whole side of the garage (about 6' high) and around the edge of the yard, which I am scared will soon collapse into the road. Thank you.

Ties are about as cheap as it gets.
The reason you see them come up for sale is the railroad is removing and replacing the old, about to rot out ones.

it gets worse. the "used railroad ties" have been known to come infested with the nastiest version of termites from the deep South.

buy new or go home is the way I look at these.

very temporary fix would be to drive some heavy sign stakes alongside the ties on the open side, and tie them to the ties with ceramic-coated deck screws.

better fix in the future would be to dig back in the yard so the dirt does not slump when you get rid of the ties and the tieback stringers under the yard, then replace with landscape border block walls, appropriately glued. don't forget drainage pipe at the inside base of the wall, exiting the front of the wall. the freeze/thaw water cycle and weight of heavy rains is what usually collapses those walls.