We paid 21$ (+100$ deposit) on Main Street for a self-converted camper, after going back and forth if we are able to hook it up (we can only hook up electricity, but this seemed to be good enough after a brief chat with the security guard). If you want to stay closer to the strip, try the parking lot behind Linq for 15$/day, we stayed there for 2 nights without problems (but we weren't to obvious about it either). It is quite far to the strip (we walked about an hour and can't recommend it, the part between Fremont and the stratosphere is a bit sketchy at night), but you can take the bus or an uber easily. Friends called the reservation at Main Street Station in advance and the cheapest rate they were told over the phone was 45$! Make sure to walk in to get the 21$ price. Good price for Vegas, especially if you want to visit Fremont street.
