some U-brakes work well, like the odessy evolver and the dia-comp 990, i've ever heard that the dia-tech brakes are failry decent as well. tektros will never work as well as dialed 990s, they flex too much. V-brakes...on a bmx bike...i've seen them on racing bikes, but i think for the most part, due to brake positioning (some companies put the brakes down on the chainstays, and others put them upside-down on the seat stays) V-brakes would not fare very well. also they look stupid. i use dia-comp 990s mounted on the chainstays and as long as they're dialed, i don't have problems. i pull abubacas, and fufanus and i hardly ever worry about whether my brakes are going to fail. another issue as far as braking is concerned is what type of rim is being used. if it's a chrome rim, with decent U brakes, everything works fine, if it's a black or silver rim, there's gonna be trouble. the V-brakes on my trials bike on the other hand...i'll just say i'd rather have 990s or hydraulics and leave it at that.
BMX bikes that are under 30lbs are race bikes that will not hold up for very long under street conditions, because they're either aluminum or thin-walled steel.
oh yeah, bunnyhopping on a BMX bike isn't about how strong you are, or how heavy the bike is. it's about the geometry of the frame and knowing how to use it...leverage is your friend.
and yes, phatman, you will get a POS for under 300, or you could get a decent frame for around $270.