At first blush, the amount you pay in storage will probably be less than the cost (and hassle) of selling what you've got and buying new when you return from overseas. 

Here are some other factors to consider. 

You're already storing some stuff -- how much extra would you pay to get a little bigger storage unit to fit the bedroom stuff? If it's not that much more, it's just more reason to store it.

You indicate you'll be gone for at least 3 months, but could it be more? I would base your decision on the MAXIMUM time you'll be gone, rather than the minimum. That will give you a conservative estimate to work with. If you might be gone a year, that could make a big difference in storage costs.

Also, consider your tax situation - maybe you want to donate the bedroom unit and write it off on your taxes. Depending on your tax bracket, it might make more sense than selling, and many charitable organizations will come and pick it up so you don't have the hassle of advertising it and then negotiating with someone over the sales price.