Another really great option that even cheaper than $300 is buying triggers for your flash gun and getting modifiers for that such as an octabox.
I think that set up for me cost me £100 in total and I use it a lot if I have to carry it through central London for a location shoot https://twitter.com/mattvogelphoto/status/1251617619704033281

I shot this cover with two of those in a stairway at O2 Islington and taped paper to the wall with duct tape... needs must!