This info used to be on TWA's website, but now one must download it to Adobe from TWA's website:

Aviators Member

With our expanded Trans World First cabin, we offer the best opportunities to sit "up front." When traveling on an upgrade, you can enjoy priority check-in, spacious seating, an upgraded menu and more.
All Aviators members who have flown at least 5,000 actual miles on TWA or Trans World
Express have the opportunity to purchase domestic upgrade certificates at any TWA ticketing location.

MILEAGE COST
0-500 $30
501-1,000 $60
1,001-2,000 $100
2,001-3,000 $130
3,001-6,000 $200

Please see the Aviators Earning and Awards Guide for purchase options and prices.
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Hope this helps.

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" Lambert International, St. Louis --- the Bermuda Triangle of the Midwest."