This is a pretty much dead thread but I'll add my two cents in case someone stumbles upon this and can be helped. There are a lot of solutions you could use. Have you tried holographic tape or a bird scare balloon? There are also sticky gels available that you can dot on ledges/branches etc that birds roost on. You can also dilute the gel with water and spray it on hard to reach places. The gel won't hurt the birds, it just makes them feel annoyed. Similar to the way we would avoid walking in an area covered in chewed gum or wet tar, birds will find somewhere else to roost (you have to reapply every year or so). Another option is a spray that contains methyl anthranilate (a safe chemical derived from concord grapes which has been used as a flavoring agent for decades). This chemical irritates the trigeminal system that birds have and gives them a feeling similar to when people are around bleach. Spray on anything they use for a food source (by the way, this chemical does not poison the birds, it just disturbs them). You can also use netting to block off the trees that they most like to roost in. I'd explain sonic and ultrasonic devices but they can get sort of expensive and since you mentioned that you couldn't afford traps I figure I'll just mention them and you can look them up if you are interested.

By the way, you're right about trapping and/or killing birds but for the sake of other readers I'll also add that they wont work. That is a treatment of the symptom rather than the real problem (that your environment is appealing to birds). Killing or trapping the current infestation will only open up prime real estate for another flock to take over.

Here is a link that might be useful: click for examples, case studies and FAQs about bird pest control