SabbaSolo wrote:
Do Piper or Cessna publish estimates for maintenance work, that repair
shops use for charging or estimating?

In Europe, many car manufacturers use estimates like this for car
repairs and maintenance work. Say the manufacturer specifies 45 min
for an oil change. That is what you are charged for, whether the
change takes them 20 min because they work fast, or 1.5hrs because the
filter broke off when they were removing it.

That's not really true in the US for repairs.

Mechanics often split the extra money with the shop, if the job is
finished faster. Here in the US, I have never seen an unexpected
problem, say corroded in place parts or interference from an aftermarket
part, not added to the final bill as extra labor with a corresponding
explanation. The estimate form itself is even preprinted with a legal
disclaimer relating to estimated prices.

Certain PM jobs like oil changes and tire rotations are advertised at a
flat rate, but even they can change. In that case, your broken filter
example would probably hold, but the paper allowing the shop to work on
the car will probably have the same estimate disclaimer.

If this doesn't exist, how does one estimate aircraft routine
maintenance (like 100hr inspections) or repair (like replacing a
vacuum pump)?

Actual time and materials. Most good aviation shops and A&P's can
provide an estimate, but it's just that, an ESTIMATE. The actual cost
will vary based on individual aircraft equipment and issues uncovered
along the way.

It's perfectly normal to be able to ask different shops what a 100 hr.
or annual might cost on a specific aircraft and get a ballpark figure.
This figure is given with the knowledge that things can change fast.

One can also compare notes with owners of similar craft on past annual
costs.