Most hydro fans are intended for extended use tbh, I'd always check with the seller/manufacturer but most of the time they know what these things are being used for and design them as such.
If you're using a kitchen/bathroom fan then they probably would burn out eventually though
I've seen people use take-out packages as reflectors, like the foil ones curries come in, but personally I'd say if you're gonna do it cheap, get a super-cheap secondhand one because light is one of the main factors in growing a plant if you get me. A plant will be stunted without a whole host of things but CAN'T grow without light and nutrition