Cost me about $250 in my moderately sized house from the same era. The difference between do it yourself & hiring someone is amazing.
Anyway, knob and tube wiring isn't inherently dangerous. In fact, it's quite safe. The problem is that it's inadequate for today's needs.
I sent a PM asking about more information on this as it was the original plan to re-do the wiring myself.
Lead and asbestos should be a greater concern than knob and tube wiring.
Lead in this area on a home of this age is basically a guarantee, although there was a lot of work to redo the home which might have removed the lead. In either case, unless I start licking the walls it isn't a big deal (especially since I don't have kids). Asbestos is a concern as you mention, however from what is visible it does not appear to have any in the home. Without ripping things up you can't know for sure though.
Why all the hate for knob and tube? If you need more power, add more lines, don't go tearing up the old house to remove something that has obviously worked fine for what, the 75 years that it has been there?
But yeah, nothing wrong with squeezing the seller for more money, that's the whole point of negotiations. I'd squeeze for money then not do the work after I bought it.
A few issues with K&T. One is no grounding which is a major concern of mine as I have a lot of things using a ground (electronics). Second is sure it's worked fine for the 60+ years since it was probably originally installed, however K&T becomes brittle (more accurately the insulation does) and that's when problems start. Then there is the question of if it was 1) installed correctly and 2) has it been modified since (and if it has was it done properly). Finally the house has blown in insulation in the attic which covers parts of the wiring, that can cause fires according to the insurance industry.
K&T works fine if a lot of conditions are met: 1) it was installed correctly, 2) it was not modified from install, or if it was then it was done properly, 3) there isn't insulation covering the wiring which prevents it from dispersing the heat that it needs to dissipate, and 4) it isn't overloaded which is possible with the electrical demands of today.