I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear about your situation.
You can sue your neighbor for trespass and nuisance. Trespass is when someone enters your property without your consent. There's no intent element to this offense, so it doesn't matter if they thought it was their property when they entered. They can be required to pay the price of restoring your mailbox and putting back your rebar and all your plants. You may also want to consider asking the judge to order them to pay half the price of a fence, because that could help make this problem go away once you get a court order.
Nuisance is what occurs when someone interferes with his neighbor's use and enjoyment of their property. Your neighbors are creating a public nuisance, and they have no legal right to do that. The judge can enter penalties against them for harassing you and destroying your property. Even if their dispute over the property line were legitimate, they're not allowed to do that. Their option is to take you to court to verify where the property line is.
"Real estate lawyers" tend to handle property closings, so that's not what you're looking for here. If you want to ask how much a lawyer would charge you to handle this type of case, try looking for a litigation attorney, or one who advertises handling intentional torts. That's what this type of case is. Because you can ask your neighbor for punitive damages, it may be possible to find a lawyer to take the case on contingency (but you can also file on your own). But you can also check sites like www.legalzoom.com and www.uslegalforms.com to see if they have anything that might help. Or if there is a law library near you, the librarians can help you find books of forms that you can use to draft and file your own complaint. You're also allowed to ask that they reimburse your filing fees if you win.
If you have any questions or concerns about my response, please reply WITHOUT RATING. It's important that you are 100% satisfied with my courtesy and professionalism. Otherwise, please rate my service positively so I am paid for the time I spend answering questions. If you are on a mobile device, you may need to scroll to the right. There is no charge for follow-up questions. Thank you.