Am I feeding him wrong ?

Hi guys, I'm a new cat owner. Recently found an abandoned kitten and have been raising him for the last 3 months . When I first found him he wasn't a picky eater at all. He would eat all kinds of foods / brands. I tried varying his diet because alot of people suggested varying a kitten's diet so that they don't become picky. I used to rotate brands for him. For dry food I only give hills. So for breakfast I would give dryfood. Nowadays he won't even eat dryfood.

Wet for lunch. For wetfood mostly I would give him cheaper brands ( purina / Whiskas ), sometimes Sheba and on rare occasions as a treat I would give hills / royal canin wetfood. Now he has become picky and when I serve him purina /whiskas/ sheba he refuses to eat it and keeps meowing till I give him hills / royal canin.

For dinner I would give him mostly sausages or cut up chicken breasts. Sometimes I'd give him chicken liver/ gizzard or minced beef. On rare occasions salmon or tuna steak. Now he refuses sausages and chciken and keeps meowing till i give him salmon / tuna steak.

Any advice ? Am I feeding him wrong?

I can't afford to feed him expensive wet food and salmon/ tuna steak every single day. What should I do? Is it better to just stick to one type of food for him? Was it wrong to vary his diet ?

How often should I feed him? How can i get him to eat less expensive food again? Any other feeding tips would be appreciated.