There is an entire section on BYC about hatching eggs. You can dig through all of that, There is a lot of discussion about what components to use.
There is also a section on home made incubators, with pictures. That's not in the forum. I haven't looked at it since BYC changed formats, but I'd look first in the learning center, so suggest you try there.
Unless you are clever with construction and electronics, you will have to purchase the egg turner. I've heard you can make one with the motor for an automatic ice maker, but that is well beyond my capabilities. If you are going to make a turner, duck eggs are rumored to do better on their sides.
I am using a repti-temp 500 thermostat, mostly because It is a plug in and i don't have to wire it, Thermometer hygrometer combos are available by the hundreds. I am using the bottom of an old coffee pot for my heat source. The top of it was hack sawed off and it just plugs into the thermostat.
You can buy the entire assembly for a wafer thermostat, but you have to know how to wire it in. Those are supposed to be the most reliable.
You can get a thermostat for a lot less than $30, but $30 seems to be the price point to get a reliable sensitive one. Somewhere between $20-$30 for a good hygrometer/ thermometer. $17 for a heat cable, or I paid $3 for my used coffee pot and 2 minutes to saw it apart. A computer fan is a couple of dollars.
I don't know what the turners cost. Maybe $30 for the inexpensive ones that will turn a couple dozen eggs. The good multi-shelf turners are lot more than that.
The cabinet can be anything from free to several hundred dollars, depending upon what you want. It has to be insulated and draft free. Even an old Styrofoam ice chest can be used. Old refrigerators, old cabinets, custom made plywood boxes, use your imagination.