[pfdietz]

Just using chemical rockets, speeds at infinity in excess of 100 km/s are possible using the Oberth effect: go into an elliptical orbit that passes close to the Sun, then accelerate at perihelion. Because the change in kinetic energy is thrust times velocity, and velocity is very high, large amounts of energy are added to the vehicle. The source of this energy is that the ejected propellant is left at low gravitational potential relative to where it was initially.

Solar sails released at perihelion can also achieve very high speeds.

Slowing down in the target system could be done with solar sails or electrodynamic sails (working on the stellar wind).

Ion or plasma engines are another possibility, with nuclear power plants.