We've tried this in the past and failed to control costs spectacularly. The JSF/F-35 project is an insane boondoggle but it seems unlikely that the alternative of splitting them out would have been better.
We all know what should have been done by this point, which is... not the JSF. But we're pretty far down this road and we do need to modernize the current air superiority weapons we have, so... eh. It looks like we're stuck.
If it had been split out into three separate programs, we'd probably have two aircraft that were "good enough" and one that was behind schedule or deficient in some way.
I'll take that over one "no, really, we have just one more round of changes to make, and then it'll be ready to satisfy everyone" fighter.
Wikipedia indicates the A10 runs about $12M. Maybe it's actually more, but there is alot of room between 12 and 81. The article also indicates that the F-35 needs upgrades as soon as it's purchased, so they are playing games to lower the quoted price.
You did ask about "modern aircraft" which the A10 is not, but that's my point. "Modern" or "Advanced Technology" is not relevant - the troops and pilots are saying the F-35 can not perform the mission of the A10 as well as the A10, so it seems to be a case of "modern advanced technology" is actually an expensive step in the wrong direction.
The A10 is completely ineffective against any enemy with modern air defenses or any enemy with serious ongoing support from such a country.
The A10 helped against Iraq, Afghanistan and ISIS (if it was used against ISIS) only because no such country had any serious commitment to the survival of those regimes.
Moreover, the A10 cannot be upgraded to be effective against modern air defenses without basically designing and developing an entirely new warplane. It would for example need new engines capable of generating vastly more electricity than the current engines can.
I'm glad that the Air Force of my country is not spending a lot of money or time and attention planning wars against opponents that will quickly lose any ability to shoot down its planes. Even if those are the majority of wars it will fight in the future, what really matters is the next war that is not like that.