Not a cam, but you might consider hyd lifters with “variable duration” design of which the Rhoads Lifter is the best known.

These improve fuel economy at highway cruise, but produce more torque after a downshift to climb a hill at higher rpm.

For ultimate “cheap” you could have your present lifters modified by precision grinding the sides of the lifter piston on two sides.

The third Rhoads lifter US Patent details grinding one or two “flats” a few thousandths deep on the side of the hyd lifter internal piston.

https://patents.google.com/patent/US4524731A/en

If you read the Patent Jack Rhoads’ father got 2 patents before this one. Jack’s son Justin got more Patents.

Improvements on the Rhoads,
of which there are many,
grind a “Trapezoid” shape on either side of the hyd lifter internal piston
or similar.

These hyd lifters do make extra noise at idle.

Some of the US Patents claim one to three MPG improvements for pickup trucks on the highway.
By law, US Patent claims are like “testifying in court under Oath”.

Any hydraulic lifter in an engine with more than 100,000 miles on it
is kind of like a new from the box Rhoads lifter
in that oil is leaking enough inside that the valve lift is shorter and over a shorter duration.