You can't do two way above 105 dB.
You need to step up the game and go three way.
But go subless.
Good woofer, good mid, good tweeter.
Lots of install effort, which as you've said you dont want due to flashiness.... but you have 18's now....
You said money is an issue.
Answer is simple: live with it till you can afford to have money to play with.