I just purchased a fish from a Thai breeder. Most people go through aquabid and most payments are made through PayPal, so you will probably want to set up an Aquabid account and a PayPal account.
You only need a transhipper if you are dealing with an overseas breeder.
I looked at different breeders on Aquabid and decided what type of betta I would like. I also looked at breeder feedback to see who had a good track record. The breeder that I liked, Ninebettas, also has his own web page. I decided that I would like to buy a copper or gizzle halfmoon plakat but he was not currently selling one. I sent him (Sathit) an email and told him the colors that I was interested in. He emailed me back with pictures. I picked one and found out the price. For Thai breeders, it's the Aquabid price, plus the shipping fee from Thailand to the U.S. ($5 in my case), plus a separate payment to the transhipper.
I read reviews on the transhippers on this site plus on Ultimate Bettas and decided to use Jennifer Viveiros (Hopdiggity). I decided to Express mail instead of Priority because I wanted to make sure the fish made it here ok. Other people on this Forum have used Linda Olsen, but I did not reach out to her about pricing.
If you purchase from a U.S. breeder or dealer, then you do not have to pay a transhipper. For example, Hopdiggity sells fish imported from Thailand is offering free Priority or Express shipping for $20. Martinismommy breeds beautiful fish has Priority for $18 or Express for $37. (If I had not promised my younger son that I would not have a betta population larger than 3, I would buy one of Martinismommy's fish).
If you ship priority, you do not get a live arrival guarantee. Live arrival guarantee depends on what the seller is offering, often the price of the fish or an equivalent replacement fish.
By the way, I have also heard of people who purchase fish at an International Betta Congress show. There are not any near me (Maryland), but I know that there is one in Michigan tomorrow (Walker, Michigan).