They should be on FilmFreeway, and the fee has been hovering around the average for festivals many years. I don’t recall if they had a specific webseries category, but Denise is very responsive to email so you can always ask her about it (also mention my name).
I’m heading to Philly TV Fest this weekend - will let everyone know how that went.
I would also recommend GenCon (I don’t know if the deadline is past). Mostly 'cause it’s GenCon. When I went the screenings weren’t super-terrifically attended (and like most cons the A/V system isn’t the most fantastic) but the staff was great and I met a lot of cool fellow geeks and fans.
One thing I’ve had good success with is augmenting the festival circuit with live screenings. My last film was a sci-fi feature, so I screened at fan clubs and bars that had screening series. I did the same thing with the webseries (the series is about immigrants living in NYC, so we partnered with some nonprofits to screen it and host panel discussions). It’s definitely another way to get eyeballs and press on your series.