Allow an insider's viewpoint on this matter.
I assume that this is a civil suit (i.e. tort action) and not a criminal
case.
Let's assume that the system you're furnishing is somewhat rare--less
common than a NEC Bungo, but more common than say, a working IBM 1401.
Further, let's assume that said system is central to the plaintiff's case
or to the defense. And that you're one of the very very few people who can
supply the system--the legal guys can't simply find another by browsing
ePay for a week.
If that's an accurate assessment of the situation, then the sky's the
limit. $1000/month would not be out of line. You may be asked to keep the
system in operating order (you can request a retainer for your time and
expenses) and you may ask that the legal folks insure the item for its
replacement cost (which can be considerable if it's rare). And, it's fair
to ask if you will be deposed or if you'll be asked to testify. If so, set
your rates up front--in writing. It's very unpleasant being subpoenaed and
not getting paid for your time.
Now, if this is a plain-Jane IBM PC-XT, obviously the pool of sellers is
larger and your advantage isn't all that great. You may have to lower your
price. But $500/month would not be unusual. And cases of this sort can
run for years--you can easily spend 2 years with motions and depositions
and recitals and be no closer to a court date when you first started.
I've served as an expert on a case of this sort. The lawyers really don't
care what something costs--it just gets passed on to the client. Heck, the
junior partner who made the 5 minute call to you probably passed on a
charge of $250 to the client.
This ain't a movie, folks.
Cheers,
Chuck