If you’re in Cali check out Instructions on how to get a BMW OL incentive - March 2019 and see if you can get an OL Code, not much time left for this month though.
Convertibles almost never lease well, they’re too rare and for that amount of money this month you would be crazy not to just go for an M3 for around the same cost.
For the 340i if you can find ex-loaners or demos (with less than 5000 miles) will be the best deal probably but I’d imagine most are gone at this point. If you go new at least you can get a little extra back via BMWCCA https://www.bmwcca.org/vehicle_rebate
Are you looking for the best possible deal on the 340i or the most bang for your buck?