I know what it is like to hate your hair. Mine is poker straight and I have to put curl in it.
I can give you several ideas to work with your bad hair days, maybe one will work for you.
1) Get a short haircut. My brother has very curly hair and he keeps it very short, which makes it very easy to manage.
2) Keep it long and wear a pony tail. My husband has horribly curly hair. When it was more than 3 inches long or more, it stuck out like Bozo the Clown. He manages his curly locks by wearing his hair long, which is acceptable these days for a man. He pulls it back, puts puggies in, as he calls them, the coated rubber type bands for hair. He puts one at the very top when he pulls it all back and then every 3 inches and it keeps his hair very nice.
Also, since his hair is long, the weight of the locks keeps his hair more in pretty waves when he washes it, combs it down straight and lets it dry naturally. Weight makes straight.
3) You could get a 'body wave' or permanent wave as it is called. Very large rods are used and when the chemicals are applied it changes the structure of the hair to make the curly kinks you don't like go away and when you wash your hair, comb it straight, you would have a more straight wave rather than the curly.
You state you have an issue with shampoos. What you want to use is a 'heavy conditioner'. I always liked a shampoo and conditioner called 'Mane and Tail'. It is for people, but also for horses. It is a great shampoo, gentle, thorough and makes hair shine. The conditioner is thick and will actually pull curl out of your hair. It always made my 'perms' go flat. It is not that expensive and can be bought just about anywhere. I also like the new Dove Shampoo though hubby uses the cheapest stuff on the shelves.
You can also use a heavy mouse or gel shaper with firm hold. Put in in your hair, comb straight and let it dry. There are some 'no frizz' products that can help tame unruly hair.
You state your funds are low. I suggest you seek out a Hair Dressing School in your area. They usually have a 'shop' where the public can come and get haircuts and permanents for much less than you would pay in a salon.
I grew up in a family of hairdressers. I worked in a salon since I was 9 and went to beauty school. I have a brother and husband with horribly curly hair.