I guess I will be the oddball here and say that I would not take him to the vet to be shaved. If he is already nervous and scared you will have a mess on your hands when you get him home. I hate the look of a lion cut on any cat, sorry. just do. I think they do too. Every cat I have ever seen that have been shaved looked incredibly embarrassed.
I have a little Persian, (in my avatar) and a big Maine Coon. Scamp, the Maine has twice the coat that Priscilla does. So I am having to brush and comb them both quite a bit. I used to be a groomer so I have the equipment to do it right. What I use mostly is a wide tooth metal comb and a mat splitter. Never, ever, ever use scissors. A mat splitter is a strange looking tool, but it is safe if you are careful.
http://purfectcatsupply.com/p-984-ma...-splitter.aspx
The very first thing I do is give them some love, and then clip their nails. Well, I do with Priscilla, Scamp is mellow, he doesn't care.
I usually rub them all over and get ideas of where the mats are and start with the splitter. Always work away from the body, and take it slow. Sometimes you can just gently pull out that mat at that point. Remember you are not cutting against the body,or across the body, you are spitting the mat and pulling it away from their body. A lot of time I just use my fingers and spread the mats in order to get the comb in under the coat.
The trick to doing this is patience. I only work on them till they have lost patience with me, or I with them. I also usually put a towel over my self to keep some of the hair off and to have to wrap the cat if they get upset. I don't try to set them on a table, I do it all in my lap.
After I get the mats out I go over them with a wire brush. I also do this slowly, more like petting then brushing. The whole things should not be a battle.
My sister used to have a Persian that she sorely neglected. The poor thing was matted to the skin and infested with fleas the first time I saw him. It took me nearly a week to get him under control, fleas, coat and personality. But when he was done he was a changed little guy. A little thin on coat, but he felt so much better and didn't hate me.