Here's my take...
Are the working part of the pens really good quality?
They seem to vary with the cost of the kit. The expensive kits tend to have higher quality, smoother mechanisms, but even the cheap kits are surprisingly decent.
Do they write with little pressure?
The same as any other Parker, Cross, or Schmidt pen.
Is the ink quality as good as an expensive pen?
In the kits I've made, the ink cartridges have been imported knockoffs of name-brand refills, although I've never had any problems with them.
When the ink runs dry can the new owner go to Staples or some place similar and purchase a new filler?
Yep. They typically use standard Parker, Cross, or Schmidt refills, depending on the particular kit.
What is the minimum cost to start (tools other than the lathe and chisels) and be able to do a good job?
By the time you buy a few kits, maybe a few blanks (you can use scrap hardwood, but the exotic blanks are sweet), a pen mandrel and some bushings, a small sandpaper assortment (which you may already have), you're probably looking a bit north of $50. Most of the kit suppliers have "starter kits" that include the basics for about that or a bit more. Penn State Industries has this one that looks like a pretty good deal for about $80. (The turning tools they include probably aren't anything to write home about, but even without them, it's a pretty decent price):
http://www.pennstateind.com/store/PKSTART1F.html
Nosey aren't I?!
Nah, just inquisitive.
And dangling your toes verrrry close to the edge of the Abyss.