If you already brew extract, all you're really missing to transition to all-grain is a mash tun. Unless you have a decent-size igloo cooler with a spout, in which case, you're not missing anything. A lot of people construct fancy false bottoms or braids, but I've found that sticking a $1.97 stainless steel sink trap over the spout works nearly as well. If you want to make smaller batches (all-grain, partial-mash or extract), you can ferment 2 gallon batches in a six gallon bucket without issue. I enjoy brewing small batches, as it allows me more room for experimentation; you just don't really need to spend much extra money to do so. You could probably stick a rubber stopper in a 1 gallon water jug, although durability might be an issue.