Ok, may be on the extreme side but will be effective and lots of media coverage.
Hire a daredevil, pay them $10k to climb up CN Tower with your company flag---really long flag...then when they get to the top the daredevil attracts all the media and they will film him jumping off with your large flag in full view.
Hmmm, maybe hire home drone pilot guys to create similar effect at night.
Fun and jokes aside.
Who is your market? Why not focus and target them based on their interest e.g. forums etc...build your brand for them to get to know you.
TV and radio will burn through your cash.
Bus ads seem good idea...but do them in the target market area.
you could try different out of the box ideas...e.g. pay the cycling team or running groups to wear your shirt or fly your banner.
provide a word of mouth incentive e.g. you pay me $100 if I refer someone to you and they buy a car...give out or email special cards for them to give out to people they know or work with...something in it for them to help you.
get a bunch of cheap Frisbees from China or those fidget things with your company info...target large parks and gatherings/outings/parades and hand out your items to the kids...frisbees never seem to die, lol
You have a limited budget, I would be focusing like a lazer on people likely to buy my cars vs. a shotgun approach.
City is busy and your bus ads might get lost in the shuffle.
Vinyl wrap your company car/cars...Addy has a nice S2000 that you know who he is and what he does.
Vinyl wrap or sticker fellow bikers since they are all over the place and get eyeballs on the bikes.
Details to measure can be based on km's they travel e.g. you pay them x per km or pay for their gas if they do x km's...you can expense all of this as marketing...therefore they are delivering the message BUT you are not paying until they achieved X (5000kms).
That's just off the top of my head.
* any use of my ideas are subject to free use of a car for a year

or $1000
good luck with growing your business
do one of those hold on to this item and the winner gets the item...ebikes or nice bicycles seem to get attention unless you are willing to use a car.
Winner is the person last standing with 1 hand on the car...could last a few days and nights. Media coverage should be good.
Add some SHOW to the event...paint balling and or water ballooning the competitors to get them to let go. Let the visitors come by and throw water balloons at them.
Serve up the hotdogs and hamburger deals...free food and water...partner with some burger place.
If you do donate a car or the USE of a car for 1 year then part of the deal is to vinyl wrap the car for 1 year.
Be Bold, Be Different, it generates attention and in this world of social media...you just provided a stage for people to show up and take pics and tweet about you.
Just some ideas!