I think the main use of the elastic IP is so that you can shut down, and start up later and go to the same location in your web-browser. This makes it dead simple to get to your ipython notebook.
However, Rachael merged my extra alias in aws-alias.sh. Check it out here:
So now you can do these steps to bring up your notebook
aws-get-p2 # get your p2 instance
aws-start # start your p2 instance
aws-get-ip # get the ip address
aws-nb # open your browser to whatever IP you happened to be assigned.
So... go ahead and delete your elastic IP if you don't want to pay the extra $5/month or so.
On the other hand... I just went and bought a GTX 1070 from newegg and shoved it into my desktop. It kind of fit with only a little interference. The cost was $400 on newegg. If I continue with deep learning, it'll be much less expensive than AWS. If I don't, I can sell it on ebay for about $350. So... either way, it's less expensive than AWS if you already have a desktop with a decent processor.