What would it cost to convert fuses to circuit breakers at the electrical panel?

If you have fuses you probably have a small service entrance amperage
(60-80 amps). You'll want to upgrade to at least 150 amps with the new
Service panel. This means pulling a new thicker entrance wire from the weatherhead
On the house (the spot where the lines from the utility pole meet your house)
To the service panel (probably need a new meter housing too).

It's mostly a labor job, so it depends where you are. In Penna. I can get a 150 amp
Service entrance (new weatherhead, entrance cable, meter housing and service panel)
Installed for approx. $750-$1,000 - this includes, of course, them terminating the existing
Circuits into the new service panel. If you have some old wiring (knob/tube or ungrounded
Armored cable) you'll want to replace that too (if feasible) with new romex, That will
Bring up the cost. What year was your house built? (that will tell if you likely have
Kob/tube or ungrounded armored cable).