Not quite the same as your typcical bad dream but similar to a nightmare in its vividness. A budget dream tends to be as "real" as a nightmare would seem but lacks the intense fear. Instead, a budget dream is more like a fairly normal dream but without any splendor, brilliance or imagination involved. Which is replaced by a real life setting or situation that seems in no way fun or wonderous, but boringly real-life and sometimes a negative experience. This is how it acquired the name 'budget dream' as it tends to be what you would call a dream, but without any fantasy or emotion, in other words cheap, like a movie lacking in the money department it cops out any special FX or narrative.
A common side-effect of a budget dream is to become confused as to what happened in real-life, and what didn't and was part of a dream, simply because the dream was too boringly real to discern from a real memory.
Weird, I just dreamt that I went to a working man's pub, and it was all full of these blokes and one guy with a beard
said "you're not a plumber" and told me to get out, talk about your budget dream.