I've used bare steel wheels laid flat under the wheels instead of jack stands. Just make sure the vehicle wheels are blocked so it can't roll off of the steel wheels if you try this. A working parking brake is nice as well. Also need to make sure the vehicle is up at least high enough that the trans bellhousing clears the frame rails beforehand so it can be slid out the side.

I don't have a trans jack. To get the trans in and out of vehicles by myself I have stacked blocks of 2x under it and then slid them out like Jenga to lower it down to the ground. Installation was the reverse. Just move the trans up one end at a time and slide the wood strips back under it and work your way back up. I went slow so as to make sure it's stable and steady both coming out and going back up. Connecting it to the engine you will have to grab it and push it into place the last bit, but it's not too bad if the trans is relatively close to the final position resting on the stacked wood pile. Sounds kinda redneck, but it did work for me anyways.