Soldering is not that hard. Unless you're 100 miles or more from an urban area, you've got a makerspace near you, and makerspaces are (in)famous for teaching just these types of skills. If you want to PM me your general location, I'll hit the directory and find one near you, or here's the link (which is not terribly user friendly) http://spaces.makerspace.com/makerspace-directory
For a battery pack, you're looking at a 2AA pack (each AA is 1.5V. They stack.) Try this one from Sparkfun : https://www.sparkfun.com/products/9547 (No association other than they're local and my primary source of electronics and components. I'm happy with everything I've bought from them. This one is tight, but it works.)
For waterproofing, silicone caulk will do the job, especially if these are centerpieces that you don't expect to use under heavy load for weeks. Hot glue *might* work, but if you're anything like me, hot glue experiments often end with cursing and strands.
Whatever your vessel is, ensure it's something you can drill through. At minimum, you have to drill through to pass the lead to the battery pack. 1/8" drill bit and a drill.
You'll also need some 1/4" flexible tubing. That's usually about $6 - $10 for 100 feet at the pet store or the hardware store or Big Blue/Big Orange/Big Amazon. And you will probably prefer to have some heat-shrink tubing and a hair dryer or a heat gun to shrink the tubing over the soldered leads. Sparkfun's heat gun has gotten a LOT of work in my house for about 6 years (I also use it to melt out varnished grease and oil from old sewing machines for restoration, and to hurry along paint stripper. And to finish 3D prints and to remove stubborn stickers. It's one of my favorite tools). Definitely worth the investment. (I paid 10.50; it's now 14.) https://www.sparkfun.com/products/10326
And here's a good tutorial: http://www.instructables.com/id/Tabletop-Water-Fountain/
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