It's great that you have so many questions, but it's hard to answer everything here. You might want to read a book like
Taking Charge of Your Fertility. That will explain everything about your cycle and how to chart your temperature, and will give you some basic information on fertility treatments.
The ovulation tests from the store work if you follow the directions and use them at the right time, and if you're ovulating. If you're unsure of your timing or don't ovulate, the tests won't tell you much. There are many signs of ovulation like changes in cervical mucus, temperature changes, etc., that are explained in great detail in the book above.
Clomid is pretty cheap out of pocket--I want to say under $100 per cycle, but I haven't taken it so I'm not 100% sure. However, it's really important that you be monitored with ultrasounds and bloodtests when you take fertility medications and those add up. I think when I did treatment (a couple years ago) it was something like $400-$800 a visit for each monitoring appointment. It's a lot, but the monitoring is so important for these reasons:
1. You want to time intercourse or an IUI for when you're actually ovulating
2. You want to be sure the dose of the medicine is correct so you're not making too many eggs (which can be painful and lead to carrying multiples like 4 or more babies.
3. Clomid has side effects like causing cysts which can be dangerous, especially if you take more medicine the next cycle.
So...those are some quick answers to your questions, but there's so much to learn in this area. I strongly recommend you check out some books on fertility. Good luck!