This basic D-link unit is not as nice and fast as the synology but it should still be plenty for basic use. »www.newegg.ca/Product/Product.as···55019CVF
You can also get single drives in network-attachable enclosures for about $150 I think. WD is probably the go to here: »www.newegg.ca/Product/Product.as···22136745
Plugging a USB drive into the router is much slower, only good for the most light use. Here are the numbers I found comparing the performance of four options:
Option - Upload - Download (MB/s) - price
Synology DS212J - 50 - 92 - $200+HD(s)
D-Link DNS320 - 27 - 34 - $110+HD(s)
Asus RT-N56U - 9.5 - 13 - $20?+HD
WD My Book Live - 45 - 61 - $130/160 1TB/2TB
The synology units are awesome but seems to be overkill for you.
The D-link is a good option if you want something a little more reliable than a single drive to store your files.
The router solution is cheap but clunky and not recommended just like you thought.
The WD my book units seem to deliver pretty good performance for the money. You don't get the redundancy you could get in the 2-bay units but maybe you don't need that to just swap some files.
Given the description of your needs the WD might be best choice. Speedy, cheap, compact. Just remember to always keep at least two copies of anything you don't want to lose!