You've got a good thing being in the travel industry. You can charge a nice rate because of this. Many times advertisers will also want to know what the percentage of users are that actually open the email. This is a determining factor in the overall price you decide to go with.
I'm assuming that if you have 10k subscribers you must have a descent flow of traffic to the site. I can't tell you for sure what the going rates are for newsletters in the travel industry but you can start with the basics... supply and demand.
Try starting off with $15 CPM for a standard banner, maybe offer a "product feature" where they can actually insert text for $25 CPM. Be creative with the different types of advertising to offer. If no one buys your ads in a practical amount of time, drop them and see what works. If you have a huge influx of advertisers, raise your prices until you can get a general balance between your inventory and the advertisers.
(I'm just throwing these CMP rates out there... Newsletter rates are always much higher than website CPM rates. So it'll be up to you to figure out what works. I would suggest trying the $15 CPM to start though, that would make it $150 per advert).
