Teletext was made by major broadcasters, so NBC/ABC/CBS in the US might have had a service. It is just broadcasted as part of the signal, so the actual hardware is in the end users device. All TV's in the UK and Europe just had teletext decoders built in as standard. The cost of entry was not high at all. The only expense was updating the content. But honestly, that wasn't really a massive effort unless you wanted a lot of graphics (ASCII style, obviously.) It was a bout as much effort as a local news paper or a well maintained BBS.
A late 80s / early 90s BBS is no comparison. Cost-per-everything in computers had plummeted by then--even kids could host a BBS with the family computer.
Per wiki on Prestel (i know it's videotex, but the article covered both):
Hosting Costs:
> In 1985, British Telecom estimated that for an IP using a typical minicomputer (such as the PDP-11) located 100 km from London and handling up to 10 users simultaneously at peak times, the one-off software set-up cost would be at least £16,000, communication costs would range from £4,280 to £5,550 a year (depending on the type of connection), and Prestel usage would cost £8,600 a year.[82]: 4
Usage Costs:
> At the launch of the commercial service in September 1979, and in addition to phone charges, users were charged 3p per minute online to Prestel from 8 am to 6 pm Monday to Friday, and 3p for three minutes at other times. Installing a phone jack-socket cost £13, with a quarterly rental of 50p. Business users paid an additional standing charge (i.e., a flat charge regardless of usage) of £12 per quarter.[23]
> By October 1982, the online usage charge had risen to 5p per minute (8 am to 6 pm Monday to Friday and also 8 am to 1 pm on Saturdays, free at other times), the business standing charge to £15 per quarter, residential users now paid £5 per quarter, and jack installation cost "from £15", with a 15p quarterly rental fee.[24]: 2
Content Distribution Costs:
> A main IP rented pages from the Post Office (initially) or British Telecom (later), and controlled a three-digit master-page in the database. In 1982, this cost an annual £5,500 for a basic package,[24]: 1 equivalent to around £29,000 in 2021.[80]
And there were no per minute costs. Teletext was part of the video signal. Every page was transmitted over and over and the TV just chose which one to display. Now expensive TVs could also cache some pages or even all 1000 (this was the max number)