Blueray dual-layer disc = 50 GB
The rest depends on the format quality and compression ratio you want to save.

I.E. with BRDL you can record.
20 hours of standard video.
5 hours of high definition data.
One BlueRay disc = five of your DVDs.

For a Gnu Not Unix - you seem very limited in your tech.

What sort of television and what country?