Just to clarify, this can be done online through their website. It's definitely policy. Here is the pricing chart:
Pricing effective April 1, 2012
1-25,000 : $50
25,001-50,000 : $100
50,001-75,000 : $150
75,001-100,000 : $200
100,001-150,000 : $300
>150,000 : $400
http://www.ualmiles.com/ReinstatementMiles.jsp
Purchase up to the total amount that had expired (only miles expired in the last 18 months are eligible)
Credit card will be billed immediately for purchase
Mileage rates and other applicable fees are subject to change
Miles are available up to the total amount that has expired
Allow 72 hours for miles to process and post to your MileagePlus account
Transaction is non-refundable
Miles do not count towards Premier status
Reactivation of only a portion of the expired miles will result in a forfeiture of the remaining expired miles
All MileagePlus Program Rules and terms and conditions apply