Pam I had a yak once it was a potomac and weighed 40 lbs, 8 foot long.
Short yaks like mine turn easier but longer yaks (over 12 ft) hold course and glide easier.
nowadays yaks are made MUCH lighter so you won't have ANY issue loading the yak on your rack
you for sure want to find a longer recreational kayak best for day paddles, fishing, have great stability for beginners (not sure on your level of expertises in a yak) the only down fall is due to most rec yak's build they don't hold course in a straight line too well, mine always enjoyed veering off my my left but that could also have been the way I was situated in it.
I would suggest poppin on over to REI and sitting in a few see what you are most comfortable then do what Paul suggested and poke around on craigslist....although just a few months ago when I was in gimpy hippy mode I found a reeeeally sexy yak at a garage sale in sun city!!!! of all places!!!
so keep your eyes open and you'll find a great yak for less than $400 EASY!
I have a soft spot in my heart for the cobra kayaks... but those cost a pretty penny. i was lucky enough to try out a brand new neon green 2013 cobra at lake pleasant back in september, Mmmmm those things are so smooth even in wake of a speed boat!