Maybe look at this from another perspective: you were looking at Imprezas, Alfas was it?, then Accord Sports, now the Mustang.
If I understand right, your budget is 300/mo plus tax $0 DAS (we all have budgets). You have $10,800 to spend for 3 years of utility and rent driving whatever.
Most leases have residuals around 50%, with 10k miles/ur you can get into the low 60s. Call your chunk 40% and we’ll make the money factor 0.00 (if you want a Ford Fusion, it’s close).
Ok your Mustang is $29,380+++ 40% of 30k is $12k which is 333.33/mo with no tax and no interest.
My suggestion is: forget whatever deals there were on BMW’s in April and May, and unless you want a 3-series loaner (you keep mentioning but don’t express interest), forget about them too. Cat food may be on sale, but I don’t have a cat.
If your budget is 300$ month all-in, you are looking at the wrong cars with no cash on the hood. No amount of lease hacking can turn $1 USD into $1.75 in Ford bucks. If you want to let loose before you had kids running around maybe look at a base WRX, base GTI, Civic Sport, something that is closer to 25k, and still bring checkbook for first payment. Or feel free to hack your own unicorn.
Another limitation you have is dealers / inventory where you are. I ran into that much more when I was in Ohio than either DC (east) or SoCal (west). Where there is scarcity, non-volume dealers (most of them) sit on their ripening bananas like it’s a fine cabernet getting better with age.