Walmart offers the Black & Decker 300-amp Jump Starter
, model no. J312B, for $39.94
. Opt for in-store pickup
to dodge the $4.97 shipping charge. (Amazon
charges the same with free shipping for Prime members; otherwise shipping is $8.80.) That's the lowest total price we could find by $10. It features a 12-volt DC accessory outlet, USB charging port, keyless on/off switch, and visual and audible reverse polarity alarms.