I am currently using ISDN from my home in San Jose. You're right in that the startup costs are the barrier--even a cheap single B channel (56K) terminal adapter for use with a serial port will run $300-$400 dollars. The telco charges are minimal in my area; $25 monthly for the line itself (115 Kbps async bandwidth). Connect charges are free for non peak usage, and $0.60/hour for peak usage time (0800 to 1700) Mon-Fri.
I am also using ISDN to get my network on through Southwestern Bell. The charges I had to deal with were: $135 deposit (refunded in 2 years) $73 per month line rate (2B+D) $350 per month for ISDN connection to another system on Internet and in Austin there is only one system that can do this for .com sites. This is a commen problem all over the country I understand. $1150 for Combinet 160 w/ NT-1 for ISDN-Ethernet bridge. $750 for account setup and for the folks at the other end to configure. This is a little expensive for home use but well within the means of even small businesses.
This is the Pacific Bell "Residential" ISDN plan. For business lines, it goes up to $50 monthly with $0.60/hour 24 hours a day.
I am lucky in that I am flat rate.
In addition to this would apply any standard long distance charges that would apply to a particular call.
We get charged only for the D channel traffic which is usually used for call progress control. In general we don't use the D channel at all.
This is an excellent setup for fast, cheap, INTERMITTENT connection to the Internet. My particular ISP is in Santa Cruz, with POPS in SC, SJ, and soon Monterey. An unlimited connect time PPP account runs $75 monthly. This actually gets me a three bit subnet so that I can put five IP boxes and an ISDN router on my ethernet at home.
It is a clean, fast (300kbs w/ compression), and economical for a full time feed as well.