Second as mentioned solid state drives are much faster but cost more ... so your cost per GB is not relevant here. With solid state drives if you need 32, always double that number... If you do some homework you will find with SSD drives it is in the speed of the read/write cycle where you benefit considerably from more storage. Also as we get into the idea of cloud computing, the carriers are making a fortune from us (just like the gas price rip off we all suffer from). The file system on iPad is not typical to PC as there is no USB port for data ... only photos in .jpg format. For movies is MOV format. So you just can't consider I'll just carry a small back up harddrive and use it that way.
Hope this helps your decisions and choices. p.s. I was planning on a 32 GB and dear wife said for $100 get the bigger one ... you'll never be happy with the get less compromise. She knows me well. Just realize there is no upgrade to more storage after the fact. What you get now you live with. In my opinion ... more is much better.