It seems that it's not pretty difficult to keep you video good quality even if you use freeware.

Alparysoft Video Quality Controller --

plug-in for media players,works in realtime with most media players (Windows MediaPlayer, for example)
http://www.alparysoft.com/prod/quality-controller.phtml

Alparysoft Cleaner for Amateur Video

removes interlace at the final stage of video editing. Applies strong deinterlace and denoise techniques, allows to save cleaned video file for your home video archive.

http://www.alparysoft.com/prod/video-cleaner.phtml

for VirtualDub

AlparySoft Denoise Filter for VirtualDub
http://www.alparysoft.com/prod/denoise-for-vd.phtml

AlparySoft Deinterlace Filter for VirtualDub
http://www.alparysoft.com/prod/deinterlace-for-vd.phtml

Any other suggestions for good freeware deinterlace?