I paid $80 for this phone at Walmart (AT&T GoPhone). It included the free year of Office 365, which is normally $70 by itself. Really killer dealer for $80.
I used the following WP: Lumia 900 til it went in the ocean. HTC 8X til it got ran over. Lumia 520 til screen shattered. Another Lumia 520 til it too, shattered. Lumia 635 for a WHOLE YEAR with no case. Paid $100 for it the day after launch at MS Retail Store. Sold it last week for... $15 to buy some gasoline. Phone took a complete and total *** kicking. Never broke. Screen was still in damn good condition after a year of hell. No screen protection. No case. I bought the bright green official genuine OEM Nokia glossy backplate off Ebay for about $11 last November after I began kicking the crap out of the original matte black one. The glossy backplates seem much more rigid. I've never had a more durable phone than my 635 with the neon green backplate. I dropped it about 3 feet on it's screen onto concrete in a parking garage. Phone exploded. Backplate and battery went flying. Screen was totally mint. Slapped the battery back in it. Popped the backplate back on. Had a good chuckle, then carried on my merry way. Zero issues. Zero damage. Indestructible. I can't tell you how many times I've dropped the phone onto a hard surface, like a patio, and the backplate and battery come flying out and everyone stares horrified and I'm just like "nah it's totally fine". I literally couldn't break my 635.
Waiting for good availability of the glossy orange MS blackplate to replace the matte black one on my 640. Have owned 640 for two weeks now. KILLER handset compared to my last 2 or 3. Absolutely massive upgrade over the 635. Can't even imagine comparing it a 520.
The 1GB of RAM compared to the 520/635's 512MB... is like night and day. Also, has a much better camera with FLASH!!!!!!!! And way higher resolution screen. Treat yourself to a 640 for $80. You'll be so totally stoked with it. Damn good price. On a side note, the 635 lacked an ambient light sensor and it drove me mad. Having one on the 640 (and 520) is quite the luxury when you've gone without one for so long.
I agree with above posters that it should be like $50 on black friday. I wouldn't suffer another 3 months over $30 price difference though.