What is the going price on new Colt 30rd preban mags?

NIW USGI 30's are going for $25 and less over at the Equipment Exchange. If you're buying, there's nothing special about Colts except the floor plate. They aren't worth a cent more than any other USGI. If you're selling, there are a lot of people that do not understand the above and will pay a $5-10 premium for Colt floor plates.

I thought I remember seeing these listed at $45-$50 on the Equipment Exchange in the past, and selling for those prices, too. I know there is no logic in it, but is there any reason behind the premiums paid for ALL Colt stuff?

Blind belief that any AR part that says colt is worth more.

Now, on some items, I'll buy colt over the import stuff (the carry handle scopes) but not the rest of it.

If you think there is a market at $45 go ahead and list it/them. Posts in the Equipment Exchange are free. Worst case is you get to keep it/them.

Point well taken, and you are 100% accurate in the spirit of your advice.  I would submit however, worth is specifically determined by what someone is willing to pay- no more and no less.  People buy anything because they either think the true value of an item is more than the value of the $ they are paying for it (either monetarily or in utility), OR they have the scratch to blow and know what they want- such as a seller with a great rep puts a mag up for sale which is harder to obtain than others.  It all depend upon if you are collecting or buying for practical use.  From a purely practical standpoint there is no reason to pay more for a Colt baseplated Okay or Universal mag.

It's pretty easy to find new condition Colt 30 rounders for $40 each and very good (used) condition ones for $30.  That's what the "market" dictates.  In my mind, that's pretty indicative of their value... at least from a monetary perspective.

Me...  I think the pony is cool, and floorplates with ponies are worth a premium.  The only ARs I own are Colts, and I like to be consistent.