Here's some pictures of my diy incubator I made from a wall shelf and put together 3 years ago. Total cost was about $20. Some of the materials I had that came from things around the house. I never had any issues with it breaking and it's easy to repair or replace parts for. Did about 15 hatches...
Since you didn't mention what type of bulbs your using, make sure to use aluminum foil around the bulb that is near the Styrofoam wall. You don't want the foam box to burn or melt.
If you don't use a fan, then it's a still air incubator. The important part is maintaining the correct temperature since the heat won't be moving much. Having your temperature gauge at egg level is very important. You can over heat the eggs if your gauges are not at that level. Also you need...