Aftermarket ECU's are not anywhere near 4k.
You can get a complete big stuff setup for way under 2500 and Megasquirt 3 for 600.
Ill be going with megasquirt this summer.
They can be. My BS3 setup cost $4k. Then again, I got all the bells and whistles, too.
Off this thread goes to 5.0 tuning.