Carvin. Look no further:
http://www.kieselguitars.com/customshop/pb_series_classic_bassesI have a JB5 that has been my main player for about a year, and it's been a great workhorse. I got the lightweight ash body option with chambers, and it's around 8.5 lb. I took the preamp out and made it passive, and it works great for me.
I love the neck profile and the B-string is -really- good for a 34" scale bass. Quality is good for the price. A P-Bass model with passive electronics would be pretty affordable.
If you want something more fancy, a Mike Lull would be my next choice, but that's in the $3K range.
Warmoth is an option, but after you are done, it'll probably cost you $1200+, and their 5-string neck profiles, as I understand, are chunky, with no option to order something thinner. Carvin 5-string necks are a joy to play.
This company below also makes all kinds of lefties, including 5-string P-Bass. You can choose electronics, neck profiles, string spacing, nut width, you name it. . . I'm really close to pulling the trigger and ordering something from them. Although Carvin has the advantage of the 10 day trial period.
http://www.public-peace.de/index.php/bass-guitars/maruszczyk/jake/5-stringAnd if you want something nicer that is between Carvin and Lull, you could consider Valenti basses:
http://www.valentibasses.com/