Some comparable monsters:
Purple Worm (Gargantuan, 5 feet in diameter and 80 feet long, 40,000 pounds)
Nightcrawler (Gargantuan, 7 feet in diameter and 100 feet long, 55,000 pounds)
Lucent Worm (Gargantuan, 5 feet in diameter and almost 100 feet long, 55,000 to 60,000 pounds)
Tarrasque (Colossal, 70 feet long and 50 feet tall, 130 tons)
The colossal monstrous centipede or the megapede would have been the closest comparisons, but they have no listed weight.
Based on the above, I'd recommend 55,000 pounds.