Can be done on Average Joe difficulty.
As stated many times, the game gets easier as you progress and level up. My suggestion is progress and save up cash for the Smashing Turnips at Shock Wave Record. If you buy 12-13, you max up your strength at 100. This increases your power substantially. With full strength you'll whip through levels and earn cash very fast. Now you can earn money to pay off Scott's Late Fees at No Account Video. Doing so will unlock the ability to buy items there, including The Mystical Head (1UPs). Also, you can replay the boss battle with Todd for a 1UP.
Utilize your shops, upgrade your stats, take a snack "to go" when you're shopping to give yourself the best advantage against the Evil Exes.