You might try checking the clssified ads in your areas such as craigs list or local message boards. Swaps, flea markets and such are also good places to find second hand bators as well. Let your friends and family know that you are looking for one and maybe even if you don't come across one they might, or they may know of someone looking to sell or give away one they no longer use. You have lots of options - you could even write up your own ad stating you are looking for a reliable gently used incubator to begin hatching. Best of luck to you!
To built comparable home made bator with QUALITY components (sorry, no light bulbs, water heater thermostats or styrofoam coolers)
you will spend at least that amount, likely more.