When I started AG I got lucky. we opened a restaurant in Colorado that had lots of old kegs for pots, cornies and Co2 bottles. My first system was gravity feed 3 tier with a 10 gallon gott cooler for the Mash tun and lauter tun and 2 self converted kegs as as kettle and HLT . economically speaking, that was the way to start, (for me) because I only had to buy 2 burners. 1 burner I put on the top "step" of my angle iron frame for HLT, the middle step had a heat shield to protect the plastic cooler and the bottom tier wasn't really a tier at all. I just let the kettle rest on the second burner. If I was to upgrade my system still more, (the gott cooler is long replaced by another keg), I woul use a pump and put my mash/lauter tun on the top with the sparge and kettle on the same level; pump the sparge water to the lauter tun and let gravity take care of filling the brew pot.