If the freezer is working, but not the fridge, then the fan between the two is either blocked with ice or has failed. Defrost thoroughly(since the ice blockage won't be visible) and try again. Most fans are installed with automotive-type plugs so if they fail, they can be easily replace once you remove the access panel. If you can get the old one out(to get the right replacement), you can get the new one in. My dad has been a landlord for 40 years and most of the time when we've had a fridge fail, it was because it needed to be defrosted.
If the fridge isn't working at all and you need a compressor or there is a leak, the odds are it won't be worth fixing, unless it's a very expensive fridge. If it's partially working but not staying at temp, then the compressor prob needs more coolant, which isn't a huge repair.
Some fridges will fail when the relay switch "arcs out." There are two contacts that turn the compressor on when triggered by the thermostat that are close to each other and in humid conditions they can partially arc which burns out the contacts. But this is less likely in a home fridge.
Any local bar or restaurant will know someone who can do the repairs. Commercial units fail frequently. Anyone who works with AC will also do fridge work. In the US, it typically runs $80-$100 for a service call plus parts.