Unfortunately you will need to buy a copy of Office for both PCs. 2 PCs is too small a group to apply for any discounts.
The question you need to ask is "Do I actually need Microsoft Office?" there are plenty of cheaper alternatives, for instance Open Office is completely free but includes most of the funtionality of Microsoft Office, but doesn't include any technical support.
Sun Star Office costs about £50, is more or less the same as Open Office, includes technical support, and you may be able to install it on several PCs.
Check with your software company to see if Microsoft Office is necessary.
Hope this helps