DC Motor For Lawnmower

[FourPenguins]

I remember seeing at some point (possibly on these forums, but I cannot find it) that power (horsepower ratings) for internal combustion engines (as in a lawnmower) do not carry over to DC motors.
This makes sense to me, given the radically different torque curves of internal combustion (peak torque at high RPM) and DC (peak torque at stall).
My question is: if I have a push mower (not self-propelled) currently running on a 3.8 HP engine, what would be an appropriate speed/torque DC motor to replace it? I'm looking to minimize cost, and I am willing to machine my own gearbox/belt reduction. If anyone has any suggestions, as well as a good supplier for an appropriate motor, I'd appreciate it.