NEW YORK, Oct 10 - Prices at U.S. farm and factory gates are expected to have stalled in September as a fall in oil prices in the first half of the month likely offset rises in the cost of new vehicles and some food products. Economists polled by expect prices to have remained unchanged in September, after rising 0.4 percent in August. The core index, which excludes the volatile food and energy components, is expected to have risen by 0.1 percent, matching the rise in August. The U.S. Labor Department will release its Producer Price Index (PPI) for September on Friday at 0830 EDT (1230 GMT).//