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?