Coming from many years experience with mountain biking, cheap and light dont go together. May want to start with a basic bike in your price range and upgrade it as time/money allows. One good thing about cruisers, there are quite a few basic upgrades which can really save weight, with tires being one of the most effective in terms of cost to weight savings. Usually most stock cruiser components are quite heavy, so simple changes like handlebars and seats can save quite some weight without breaking the bank.

One thing I found out recently, cruiser bikes with gears tend to lean more to speed vs hill climbing. Was surprised with a recent 7 speed purchase in that I would consider only 3 of the gears usable. Wound up doing some gearing changes to get a bike better suited to climbing moderate hills, see the post "Gearing for 7 speed questions" for more info.

hope this info helps.