United Airlines appears to have launched Premier Qualifying Miles (PQM) and Segments (PQS) sale.
Mileage Plus members can usually add PQMs to itineraries they have purchased on United and the price tend to vary.
You can access this offer on United’s website here.
Note that you must also meet the Premier Qualifying Dollars (PQD) requirement.
This offer was not available for my account so cannot see what kind of prices it may offer.
You have to keep in mind that it is still early in 2019 and, although it may seem tempting to buy PQM and PQS at this time, you may not end up needing them at the end.