Note: This procedure requires editing a game file; creating a backup copy of 
the file before proceeding is recommended. 
Use a text editor to edit "mission_[number].qst" file in the Folder: 
"\Program Files (x86)\Kalypso Media\Airline Tycoon 2\init\quest\mission\<mission>".
Find the following section near the bottom:

< type.st >initializeplayer< /type.st >
< name.st >player</name.st >
< deposit.ll >100000000< /deposit.ll >
< addictionaggression.f >0.85< /addictionaggression.f >
< addictioninvestment.f >1.00< /addictioninvestment.f >
< addictionquality.f >0.65< /addictionquality.f >
< addictionredemption.f >0.55< /addictionredemption.f >
< nolocationjump.b>0< /nolocationjump.b >
< nomarketing.b>0</ nomarketing.b >
< noorders.b>0</ noorders.b >
< noordergeneration.b>0</ noordergeneration .b >
< norandomevents.b>0</ norandomevents.b >
< nosabotage.b>0</ nosabotage.b >
< questlevel.ul>12</ questlevel.ul >
< /post4 >

Change the value of 
< deposit.ll >1000000000</ deposit.ll > to whatever desired. Save the file and 
load a new mission or start a freeplay game.