I haven't found one. Like the other posters, constant searching is the key. That includes not just looking at regular business fares (Yapta alerts help with that), but also constant checking for UA R class, and also searching different connections. It seems hard to find business flights TATL in the $4k and less right now that are directs to the major cities, though I found an IAD-CDG for $2.3k around Thanksgiving and an $1.1k upgradeable with miles at booking for IAD-BRU next March. My travel dates are usually pretty fixed, which does not help, but my company does pay the cost of economy, so I have a real incentive to find the cheapest way to upgrade. If I didn't get miles for my business flights, though, I'd probably just get award tickets more often and get the copay reimbursed.