So you are currently brewing 5 gallon batches and they keep turning out so damn good. You start day dreaming about upgrading to a 15 gallon or larger system. This is something that most homebrewers eventually go through. The problem is, most of us lack the funds to upgrade to that larger system whenever we feel the initial urge. Our extra cash is usually spent on craft beer mix packs that we refuse to give up. There is no reason to max out your credit cards and drop 2-5k on some fancy stainless steel beer brewing system. Upgrade layaway style! Slowly buy the small things you need to upgrade to a larger system. Doing this will also give you the opportunity to learn each component as you attain it. Being creative is another great skill to unleash!
How about a CHEAP fermentation upgrade idea?
If you buy homebrew supplies from a local supply store, you probably have a decent relationship with the employees. These homebrew supply stores usually have Briess liquid extract barrels that eventually become empty. Considering their priority is putting more extract out, these empty barrels get tossed in the garbage. Ask them if you can have their next empty container. They may have some sitting in the back waiting for you to ask.
The smaller extract barrels are what you are looking for. They are food grade. They have a liquid scale on them, they have openings on the top, and they have a damn good handle! 15 gallons of beer is not easy to toss around. All you need to do is install a #13 rubber stopper with an elbow for your blow off and you are good to go. These types of barrels are plastic so you will need to make sure you have optimal temperature control during the fermentation process. If you can manage that, your beer will ferment very good inside of one of these.