It doesn't have to be new, it just has to be reliable and hard hitting.
.357 magnum and up revolvers will probably do it.
10mm will probably do it.
Looking at gunbroker I see that there are guns available in suitable calibers at or very close to your price point. Don't forget though that you will also need to buy some sort of holster for it so if that price is a hard limit you will pretty much have to take what you can get. It won't be the lightest and it won't be the specific gun you had your heart set on.
The glock 20/29 would be my autoloader choice. I don't know if you can get holster and gun for the desired price.
Some sort of used ruger or s&w revolver would also get the job done. Taurus probably also works.
A ruger blackhawk is nothing to sneeze at either and might be a good choice for the desired price.
Here is one with included leather; an auction price starting below your limit and a buy now only slightly over the limit. It would do the job.
http://www.gunbroker.com/Auction/ViewItem.aspx?Item=513663687
To stay within the budget you'll need to do some hard searching I'm afraid. It'll require a bit of leg work checking out the pawn shops and dealers with trade ins.
I don't know if there is such a thing but maybe someone would rent or lend him a suitable gun for his trip. That way he can get exactly what he wants when funds become available.
Failing that there is always bear spray if he is willing to compromise on the gun bit.... or a shotgun with slugs if he is willing to compromise on the handgun bit.