Go get a storage-unit - this used to be my go-to when the other musicians or I did not have the ability to accommodate our practice sessions.
You'll want to shop around - the availability of on-site electricity can be an issue. Also, be transparent with the owner - you may need to negotiate a somewhat higher-rate for said energy consumption... (Point being not to leave a bad-taste in the owner's mouth [and/or be unceremoniously kicked-out] when they realize you're paying them $70 a month in rent but, consuming $50 a month in electricity) But, luckily, you'll usually find that your cost will be MUCH lower than what your average music-house will charge for storage and time. This is a cost effective solution, even if it's just you renting the unit.
Besides this, there's the issue of noise. You might find that this is less of a bother to the owner and other tenants due to the fact that most of these places are graveyards - people are usually in and out, not coming to the place for either solitude or socializing. If you're still afraid of it being an issue in the urban environment, you can egg-foam the bejebus out of the space.
Finally, your average storage facility has decent security - fencing, a camera system, and they're usually on the radar of your average beat-cop... Get a beefy, cut-proof lock too.
*Warning: You may be left wanting for a bathroom. :P