Hi. What I have done on a "extreme low budget",I bet I got near $75 in the cooker now.. that carboy cost me $45, so I am pretty satisfied with that.. of course I have a stainless-tig welder here, plasma cutter, and hillbilly engineering. I'm a 56 year old electrician-instrument tech. (disclaimer) What works in industry will work in a home-brewery. People here on the forum have helped me (why I am here), shared information with me and I do appreciate it. My way is not always the right way, or the only way, it is just how I did it.
I am against a immersion element, well, heat transfer, there immediately at the element you have a "hotter" temp and cooked on "caramels" and other things that will not clean as easily, discoloration.. and normaly the elements are aluminum encased(my stepmom died with alztimers?) Yeah, I know.. ALL the brew experts recommend them. They are quick and easy to utilize. (and expensive) ANYTHING in the pot you can not scrub is dirty.. threads, elements, pump hoses.. etc..
A $7 220 volt oven element can be reshaped before it is heated. I did that, a PID control off ebay with SSR, and thermocouple can be as cheap as $35. Since you are using a plug disconnect, a power relay like I put into mine is not needed. Put it under the pot, close it in with insulation, heat rises into the kettle. If I do it again? I'll have a cooking area I can swap for a smaller stock pot also, and the pressure cooker for jelly, and (heating and shaping hdpe) and...
Insulation, well.. keeping the heat "where you want it" is just good common sense (economy and room cooling-house comfort). you can aluminum flashing-metal wrap the cerwool-mineral wool or do a hard cover like I did with a old tank. Recently I took the lid off mine during the chill-out (steam rolling out) and the upstairs temps went to 76 immediately.. My wife opened the basement door and hollered at me. (she lives up there and I was in the dungeon-brewery) Another option would be to hook up with my insulator buddy and have him sew you a high temp insulated blanket to velcro around it. He does that for companies all over the USA, he is a biker, a drinker, and one of us.. Has a sewing machine, a roll of temp matt, and bales of mineral wool there in his workshop, he wraps boilers and chemical plant piping all the time, he can cut out and sew faster than I can draw on paper.
Keg-stock pot.. well.. I had one gave to me, plasma cut the top, welded a ring on for a lid (could have cut it that size) but then I'd scrape my arm reaching into it on the edge cleaning.. welded a drain spickot 1/2" stainless into the bunghole for drain.. with the "channels" it has made into that end of the keg every drop comes out the bottom. Threads hold funk and "bacteria".. so I tried to run the temp sensor from the top.. going to put a nut on the side to hold it against the tank, under the insulation and read it there.. thou... Not the best, a immersion probe is better. After thought, I raised my cooker drain up to 20" off the floor to drain into the carboy. Did that yesterday by welding on angle iron legs.
Getting the "juice" wort out of a grain? Right now I am using brew in a bag, it works.. but I dislike the bags. well how about a double boiler?? I'm still looking for a pump, bought one off ebay I thought was the size of a tea kettle, it fits into my pocket. THE stainless stock pot drops into the top of the keg, has a coffee filter made into the bottom in the home made drain system. There will be two temp sensors, one in mash stock pot, one in kettle a switch to choose.
Ventilation, well.. making jelly, making beer, the steam off it is "sticky" and over a period of time you'll get attacked by vermin of all types, bugs, rats, mice hunting grain and sweetness.. I'm working on that here, a old range hood I have stuck back with a vent fan. That should help with the steam problem also. (I have had my beard "crusty" from standing stirring home made jelly, 55 gallons of free apples)
I'm still learning the process, and working the kinks out of my system here. I have a old 1990s automation set that can run it all by laptop, or upstairs computer.. if I decide to go that way, Manually works, I spent most the brew time on the couch Saturday, the PID electrically keeping the temp "EXACT" so I didn't have to stand there and fiddle. (brew schedule, After wort in a bag, do this 60 minutes, do this 30 minutes, do this 15, chill.. )
Video Link: http://www.youtube.com/watch?v=6sxrC9PxXAM My Saturday batch in the carboy now.
You really want to go "Cheap redneck"?? get you a old kitchen stove, take the cooking top off it, cut a hole in the top of the oven to fit your pot so the bottom will drop into it, fab a stand inside the oven for the stock pot to sit on, there you are.. instant heat source, heat control is a knob- remote bulb inside the oven, 4500 lower watt element in place, cooking vessel in place, insulated, ready to go. Discard the left over pieces. I've had several kitchen ovens gave to me over the years.. can't get much cheaper than that. If you fab a trap door to go on top? well now.. you could bake biscuits and dinner rolls too. Post pictures please. (I baked some home made bread last week with HOMEBREW)
All this typing, I got to get the old Harley out and go for a ride in between thunderstorms. Cheers, good luck.