Having unrealistic expectations about how cheap and how fast you can get up and running is a surefire way to end up spending way more money than you thought you would. That sounds like such an obvious thing to say but it's something that needs to be said for anybody opening any type of business. There are a lot of guys out there who think they are going to open a nano and do it on the cheap because they're going to work part time and they'll just wheel their homebrew set up into some warehouse space and build a tap wall. Then they are surprised when the local authorities say no propane burners in the building, you need to construct drains, comply with ADA regulations, local health and safety code, zoning issues, etc. and once you get past all of that then you can start worrying about your brewing permit. All of that means you're buying equipment and paying for a lease for months before you can brew and the longer it takes you to deal with issues you didn't know would come up and don't have the funds allocated to handle them the more money you are losing up front before you've poured a drop of beer.
I'm not saying you can't start a small brewery on a limited budget because obviously there are many who have done it or are doing it but for every one nano out there operating at a profit (or even breaking even) there are dozens who are still trying to get off the ground or gave up because they didn't do the planning up front. The start up process for a brewery is primarily a legal battle and a race against time to start selling beer before you run out of money.