Call a few electricians and see if they have any boxes that they would give you.
Collect styrofoam that electronics are packed it, paint those with black latex paint. then drybrush or spray paint them with metallic paint. Attached to a wall they look pretty neat
Old satellite dishes (the big ones) are easy to get now that they are out dated, post on craigslist that you remove them for free, an 8 footer could make a neat dome roof or set it up as a dish in or on top of your set.
Try to do more with shadows, LED lights are great for that because they do not oscillate or strobe they give great crisp shadows. Put a small piece of chain in front of it for a decent lab shadow look.
Build a box out of 1x6 drill 2" and a few 3" holes Regular glass bottles put in upside down with liquid inside look pretty good.
Bubble towers are pretty easy to make and there are some good tutorials online.
Good luck on your lab,