Didn't you say that you already have a jacket, helmet and gloves (although not the newest)? If that's the case, then I'd get a tire(s) because that one (those) will need to be replaced soon. But if you do get $700 out of the dirtbike, you should be able to afford the new tire(s) and pants. The Joe Rocket ballistics will be good enough for normal street use. Trust me, jeans won't do squat. I'd rather have an old (but sturdy) jacket and good pants than a new jacket and a pair of jeans.
Also, after buying the new tire(s), remember, they will be VERY slick for the first 60-100 miles, so don't get wild leaning into turns. Slow and easy on new tires.