So, here's one.

A close family member just moved into town.  She wants a tree to grow in a pot on her deck, and I'm giving her a VdB for her small 2nd-story balcony. 

She's forgetful and sometimes leaves town for 7-10 days at a time, so self-irrigating is required.  It also has to be nice looking in order for the HOA at her 2-story condo building to allow her to have it.

Does anyone know of anything out there pre-fabricated, looks nice, and comes in a 20-30 gallon size which requires minimal assembly that may be available for purchase?

You might look at the auto pot system, or use just the auto pot smart valve with a larger container.  The smart valve waters only when it's needed and feeds from a reservor. 

http://www.autopot.com.au/ and look under technology for auto valve mk 2.  Smart drippers are another choice.  There is a USA distributor.  The product looks interesting but I have not tried it.

An alternative would be micro irrigation.  I've used this with orchids and it works well.  A battery operated timer installs on a water hose outlet, then the tubing and the emiters distribute the water.  A decent timer is about $50.  It does require a small tubing about 1/4" from the faucet to the plant(s); which is likely the biggest drawback.  My system ran flawlessly for several years. 

You might want to try the Walmart self-watering containers.  I think I have one that is 20 gallons, but not sure.   If it's hot, it would still need to be watered every day.  You could get a simple drip system that attaches to a hose and put the drip in the reservoir so it will get watered daily.  That's what I do when I'm traveling.  

I forgot to add:  she has no water spigot on her back deck, so solutions can't revolve around drip irrigation.  There is no way they will let her install a hose bib on the deck, even though she owns the place.  Intown condos are crazy about rules.  No water spigots, no grills, etc.

http://www.gardeners.com/Adjustable-Reservoir/34-507RS,default,pd.html?start=4&cgid=PotsPlanters_SelfWateringPlanters

I found this, I haven't seen these before so I don't know how they work but maybe it could be an option.

Touching base on this - Ikea has a self-watering kit for under $20 at their stores.  I found it while there picking up cheap terracotta pots for some deck plantings this past weekend.

You may want to amend your soil mix adding in more perlite or something similar