As a compromise you could run extension cords thru 3/4" grey pvc conduit along the ground, at a $1.35 a piece it only costs about $80 bucks in pipe, and either leave it above ground for now or bury it shallow.
If your pump draws less than 300 watts I don't think there would be a problem.
Running extension cords in conduit is generally not a good idea(Maybe for very short distances).Having insulated conductors inside an insulated jacket inside a conduit does not allow for heat dissapation(heat being a big enemy when your talking electricity).That would get into a whole other issue with derating your insulation value.
