What's your favorite mod you've done for under $250?

$250 is about £170, so would have to be the traction control link on the rear of the MG.

Remove cat back : free

Blinker fluid. $50 for 5 gallons at my local BMW store.

Angel Eyes on my bimmer

I literally have a ram air intake made out of duck tape and weight reduction

New stereo and changing out the front speakers for better quality ones, really helps to lighten up long trips and/or traffic jams.

Speakers from the junkyard I found for like 30$

I changed the rear springs of an E10 Corolla hatchback with heavy duty ones for a wagon version. the result was a a rideheight that was so high and a ride so stiff, you could haul 5 people and 6 crates of beer and it would look as if it were stock. the Whole mod cost me €90 and a bottle of Johnny walker.
https://d37nk263jfz2p8.cloudfront.net/image/1/1200/0/uploads/garage/wp_20140518_16_11_46_pro-553404520def2.jpg

Tesla owners be like

“Software updates yo”

I don’t have a car but the best mod under $250 is defenatly a better driver.