An issue with my music video - Fog/Smoke Machine

In my music video i wanted to use a fog machine to give the feel of being in a dream however i am unsure of that happening for a number of reasons

• I don't know where to find a smoke machine with the budget that i have in mind, i don't want to rent one out for £35.
• I'm not sure if i am aloud to use a smoke machine in the school building because it might set off the fire alarms. 
• I have asked alot of people if they have a smoke machine or know where to find one and nobody had any clue of where i can get one from. 

That gives me a couple of options, i can keep asking around until i find one, i could rent one out for a ridiculous price or i can use editing techniques to give the impression of fog, which i wanted to do regardless of having a fog machine.