It really depends on the neighborhood and how often you need to move your car.

If you are only using your car on the weekends, and live in a neighborhood where there is street parking, you may be OK. You might have a tough time finding parking when you get back from wherever you are going, but you can at that point I guess pay to park somewhere overnight and then move your car in the AM.

I live in the North End. I just got a car. I can't even get a spot in the lots nearby because there are waiting lists (I'm on them). Lot spots cost $400+/mo. I use my car every day and generally need to find a spot between 6 PM and 8 PM, which can be brutal sometimes. I would say that 50% of the time, I find a spot within 10 minutes. The other half of the time it can take up to 30 minutes. Often I end up parking in a spot where I have to move by 7 AM (construction zone) or 8 AM. I'm up anyway so I end up moving my car in the AM. I hope I get a lot spot soon.

I used a combination of rentals and Zipcars for 15 years. Rentals are $$$. Zipcar is really terrible.