They can be worth more, but there are also many common ones (N.Y. Central Railroad, for example). If he is allowing you to cherrypick at that rate, there may be some deals to be had on scarcer items, but if that is a bulk rate price, I would be careful.
Insurance cancels, in general, are not as in demand as railroad, but there are some scarce cancels (some of the independent insurance agent cancels can get pricey, the Howard Insurance Co. cancel in green ink is quite scarce, Phenix is a good one, etc.).
The more ornate and elaborate the cancel (in general), the more valuable it likely is.
Here are links to several 1st issue cancel collections I have purchased (no, they re not for sale). If any of the cancels correlate to ones you are considering, I might be able to give you my impressions. Bart as well.
1. Railroad, mining, and misc, purchased in 2009. I pulled some keepers out and then flipped the remainder.http://www.revenue-collector.com/HeritageColl/
2. Insurance. Purchased in 2011. Still intact. Many identified by Tolman numbers.http://www.revenue-collector.com/insurancecoll/
3. Railroad, proprietary, steamship, playing cards, etc. Purchased in 2011. Still intact.http://www.revenue-collector.com/railroadmisc/