Not 1 wire but a good answer to RS232 limits is RS485. --- note that Dino got in while I was typing this.... 800m! Wow!
I have no part in this store except I've bought from there twice with no problems:http://yourduino.com/sunshop2/index.php?l=product_detail&p=317
MAX485 RS485 Transceiver (Pkg of 10)
Your Price: $2.00
The shipping is not cheap **compared to the knock-down chip prices** so I end up picking up extra chips usually 5 for 75 cents to a buck and a half. If you do order there, spend some time browsing the stock and bargain bins as it were. You might get ideas.
Another thought that might help or not is that if you're using CAT 5 then you have 4 pairs that could run 4 1-wire buses. With many devices adding to the 'weight', wouldn't distributing them be one way to increase the working length?