$100/month is a pretty low transportation expense. If you buy a car, you're going to spend more than that for the next few years, but if it was a used car, you might pay ~$250/month for 3 years and come out ahead in 8-10 years.

If you go for a new car, you could easily pay $600/month - at that point it would take > 18 years to break even.

Of course, there are other things to take into account: convenience on the one hand, maintenance, parking, & insurance on the other.

But, my gut instinct is that you'd be better off to keep taking uber and invest the difference in an index fund. Keep that up for long enough and you can buy a new car in cash (or retire early).

[edit]: Don't forget that you can bicycle also. A $400 bicycle has an incredibly high ROI if you replace a few regular car trips with bicycling. It's a net gain for your health too! (You may already be doing this, but it's worth pointing out anyways ;)