We used to see a behavioral/speech therapist for my daughter's food aversions. I know that they deal with these things every day. They had a big sign on a wall that said "Mealtimes are NOT supposed to be a battle!". I know they worked with lots of kids. Even in your insurance might not cover it, it might still be worth 2-3 sessions just to cover the basics- see what you're doing wrong, what you're doing right, etc.
But I do remember the basic things she went over with us on the subject.
1. I know she told us NEVER to hold the spoon or fork after age 12-18mos old. I know I still do it sometimes (daughter is 2) and it is "my bad". It somehow leaves it open to the child to create a game out of it.
2. To never ever make special food for your child. Serve them what the rest of the family is making.
3. Your child will not starve. They will eat when they are hungry. My dad grew up in post WWII Germany and his mother will vouch that she never had any of her children turn down food. If he's not eating, he's just not that hungry. All it will take is a couple meals where he goes without food and you do not give in to his whining for the food he prefers instead, and he will eat. Remember, this idea of making "kid friendly food" came about recently, and so did picky eaters because of it.
4. Does he snack a lot? The therapist said snacks should be kept very small, even avoided completely if the child is a poor eater at mealtimes.
5. And dont "harp at him" to finish his food. Set a span of time he's allowed to spend on his meal, say 30 min, and then when its over take the food away. You can give him a warning that he only has 5 min left, but he'll get the point after a meal or two. Use a timer, not your voice, to get him to finish. If he says he's done, then he's done though.
I know its hard. I really have been through it, though my child was a lot younger. She didnt eat food from a spoon of any kind until a 10mos old, finger foods until MUCH older. It turned out that even at her young age, a lot of our problem was not her gag reflex but her manipulation of us, even at that tender age. My sister-in-law went through exactly what you are describing when her son was 3 y.o. It can be better. If you need more help, there is professional help for these things, good help, out there.
Best of luck! Hope some of that helped!