When you say Fairfax/Loudoun, have you looked in Chantilly? Toll Brothers is building condos there that would fit in your budget:
https://www.tollbrothers.com/luxury-homes-for-sale/Virginia/Commonwealth-Place-at-Westfields/The-Fairfax

If you’re open to Ashburn, then there’s townhomes in Brambleton:
Downtownbrambleton.com

No, supply is unusually low as you noted, I wouldn’t assume you’ll be priced out

The resale market in Arlington is tanking

Loudoun has a much less sustainable market. Unless you can negotiate large concessions from a builder, buy a newer resale

Sorry I was referring to new builds.

What area are you looking at? There are several larger condos (1500+ sq feet) that have been on the market for almost a month across the street from the Dunn Loring metro. They are mid $500. Low condo fees given the size of the unit. Typically, these would be snatched up right away, but have been sitting and don't know why. You can probably negotiate a bit and use the leftover to do some updating.

There are 3 on the market and here are two for example. https://www.redfin.com/VA/Vienna/2653-Park-Tower-Dr-22180/unit-306/home/172949246

https://www.redfin.com/VA/Vienna/2665-Manhattan-Pl-22180/unit-312/home/172979030

DH and I started casually looking 6 months ago to buy a condo in the Fairfax/Loudoun area and get out of the city. The prices in that time have already gone up about 30k and are approaching the 600 range. I am shocked that they continue to rise this quickly, and am wondering if our window to buy is closing? Realistically will they continue to go up? Our budget is 650 so at this point we are getting close. There is nothing on the market and we are priced out of new townhomes, so really the condos are the only smart option.