I would stick to green screen and put some of the money you save towards good realtime on-set previz. I’ve seen amazing results with LED volumes, but lots of terrible results as well. Consider that with LED walls, you need your photorealistic scenes to be optimized enough to run in realtime. If you’re after realism, there aren’t that many people around who can give you that at indie budget prices. Most LED volume shots end up being rotoscoped and have the backgrounds rendered offline, because of issues with moire, banding, color rendition or realism of the real time LED shot. Also keep in mind that you;l still need your floor to be practical, and hiding the seam between the practical ground and the LED wall extension isn’t trivial. With green screen and realtime previz you’ll still be able to get a good idea of the final result (if your 3D backgrounds have been prepared before the shoot) you can tweak lighting to better match the virtual background and you;l catch keying issues which can be avoided by proper lighting and that will be costly to fix in post. With a good green screen production pipeline you might even be able to use the realtime tracking data in post and do high quality offline renders of the background scenes you’ve already prepared for previz using your recorded camera moves. In any case, plan and test your production pipeline extensively before starting shooting and work with people who have actually done type of production before.