If you only have $150 and you can't find a way to earn enough to buy a full box, your options for searching halves will be pretty limited, especially if you only have access to a couple of bank branches. If you can develop a good relationship with the lead teller you may be able to talk them into ordering you a box and allowing you to buy $150 at a time, but don't count on it.
What are you searching for? If you are in this just for silver, I would say do dime rolls and keep asking for halves whenever you go in case someone happened to turn some in. I wouldn't bother with quarters since they rarely produce silver. If you have an interest in coins beyond silver, you could always do cents or nickels and try to build a set or pull key dates.
One other option, which would be a lot of work, would be to do cents searching for copper (pre-1982) and when you get a large amount try selling on Craigslist or eBay. You could probably get $0.02 for each copper cent you find, and a typical box will run between 18-25% copper. Add that to your coin fund and eventually you would get up to enough to buy a box of halves if you really want to. If you are just searching to make a small profit this would be a way to do it with mostly sweat equity but little cash outlay.
Just some thoughts. Happy hunting!