New to terrariums

[Rhonda Svoboda]

Okay, I've been growing orchids for several years so I've a bit of experience. However, I recently aquired 4 species Phal.'s
They are not handling the winter temperture in my home like my hybrids and I am trying to raise both the temperture and humidity to get them through the winter.
Space heaters are out due to electricity costs. I ordered a heat mat but I am thinking it won't warm the ambient air temperture.
So I am considering a terrarium. I should say that I grow these under grow lights so the terrarium has to fit on my plant bench.
I've looked online but I can't find anything large enough that's in my price range. I am considering buying an aquarium but I am not sure how to cover it- maybe plastic? Would I need a heat lamp to warm the aquarium?
Any and all DIY suggestions and advice is more than welcome. Please