Either you are misreading the model number (easy to do) or it is mismarked (happens quite often) as the 29 is a 44 Magnum. Check the model number again carefully and the caliber should be on the barrel. If it does say Model 29 and the barrel has 357 Magnum on it then it is likely a mismarked Model 27.

Either a 29 or a 27 will usually be worth between $500-$1,000 depending on exact model and condition. A very early 29 will be worth more. The long barrel is least popular and hurts value some.