You are correct that the only longterm airport parking lot is at DCA.

It's certainly possible to find on-street in Arlington and then take Metro to the airport, but be aware that finding an unrestricted space isn't that easy in the neighborhoods near DCA. In fact, much of the street parking in Arlington that isn't metered is zoned and restricted to residents of that zone.

I am aware of unrestricted parking on surface streets not that far from the Ballston Metro Station, but that'd require a change from Orange to Blue at Rosslyn, and if you're not traveling during rush hour, it could take almost an hour to get between Ballston and DCA.