We've just installed this and it all works fine, except the value in our local currency (SEK, or Swedish Krona) is not displayed in the text field. If I enter a number and save, the next time I look at the subscription, the value is 0 (zero), but if I look in the database:
a:1:{i:0;a:6:{s:4:"cost";a:6:{s:3:"sek";s:4:"5.00" ;s:3:"usd";s:4:"0.00";s:3:"gbp";s:4:"0.00";s:3:"eu r";s:4:"0.00";s:3:"aud";s:4:"0.00";s:3:"cad";s:4:" 0.00";}s:6:"length";i:4;s:5:"units";s:1:"D";s:11:" ccbillsubid";s:0:"";s:18:"twocheckout_prodid";s:0: "";s:9:"recurring";i:0;}}
Which looks correct to me, at least :)
I have double and triple checked the edits in the php files, but can't see anything wrong there.
We're on 4.2.2 (brand new install, we're moving from phpBB).

Did you do the database changes? If so, can you post up the contents of your forumroot/admincp/subscriptions.php file? Maybe in a private pastebin.