Basically, you’ll have to start by contacting a local
rat & rodent control expert or two and asking them for an estimate. It’s a delicate job, so it would be a bad idea to go with the cheapest possible option here, as that might result in the rats not being entirely eliminated and you having to waste time and money repeating the process. If you live in an are where rat infestations are relatively common, as someone you know and trust to refer you to someone they’ve gone to and been satisfied with. The experts will then propose one or more removal methods that might include poisoning the rats or simply setting traps for them. You should pay special attention to the types of poison or chemicals the exterminator proposes, as some could be potentially very harmful to small children or pets if accidentally ingested.