If you already have a kettle big enough and heat source powerful enough to do a full boil, you can already do BIAB with the purchase of a big grain bag, like these guys said. And if your heat source isn't powerful enough, you can still do partial boil BIAB, you'll just have to take a big hit on mash efficiency since you won't be able to sparge enough (or mash thin enough in the case of no-sparge BIAB) to extract all the sugars.
If you want to go the more traditional route, don't think you have to purchase a fancy pump-driven three tier set-up. You can buy a 10 gallon cylindrical drink cooler from the hardware store for cheap, buy the bulkhead/ballvalve parts for fairly cheap, make a braid or manifold for cheap (although I'd just spend the money and buy a false bottom personally, they're much less prone to failure and much more efficient should you decide to fly sparge), and then you'd need a second kettle for sparge water. I have a 10 gallon boil kettle, a 10 gallon cooler MLT w/ false bottom, and a 5 gallon kettle I use as HLT (and an auxiliary 3 gallon kettle that I use on occasion if I'm doing a larger batch or a partigyle or decoction mash or the like, but don't need it for most beers).
You don't need pumps or a tiered system, just a table or counter. Pumps make life easier, but if you can lift things up and down, that's all you need. All my brewing is done between my gas stove, my kitchen counter, and my kitchen floor.