IAD-AMS United Miles Upgrade

I will be traveling with my family to the Netherlands next summer (MDT-IAD-AMS). I have enough miles for the three of them to fly business class. However, my flight is covered by work and an economy ticket is the only option for reimbursement. I found an economy ticket for $1300 and was going to use miles to upgrade and sit with my family in business class. The fee each way is $550 (in addition to the required miles). Given than a ticket using only miles is 100k miles, this seemed quite expensive. Are there other options? I wanted to see the price if I just paid for the upgrade, but I couldn't find it without booking a ticket. Any advice on the best way to do this?

Thanks in advance.