The pages were send one by one so if you typed 200 you would have to wait for page 200 to cycle by. If it had 100 sub pages you would have to wait 100 times as long. I believe more important pages could be send more often or similarly the cycle would skip less important pages. Decent TV's would just store pages and sub pages until the next cycle.
I asked crappy local TV stations what a page would cost but they didn't have anything under 1500 guilders per month (comparable to $1500 today) which was an absurd amount of money for 1kb of hosting.
No wonder that, besides news, subtitles and the tv guide, the thing was entirely filled with lottery phone lines, astrology lines, sex lines and similar trash.
$1500 today is probably in the region of 10s of GB, sure, but that's almost a commodity volume by comparison in terms of supply.