Partly depends on how long your experiment needs to be exposed to microgravity for. If you just need a few minutes, you can get a flight on a suborbital sounding rocket from Wallops Island, or Blue Origin's New Shepard. If you need longer than that, you can probably looking at booking something on the ISS (if you need human operators) and/or one of the cargo ships that carry things there (SpaceX Dragon, NG Cygnus, SN Dreamchaser (coming soon)) if you don't. Which one you want depends on how long you want the experiment up there for and whether you need the equipment back or can just get your data remotely and dispose of the equipment. If your experiment is small enough and you don't need the equipment back, you could also put it on a cube sat and either get a rideshare with other payload(s) or get an Electron launch.