What type of snake would be best for some one wants to switch from keeping lizards to snakes?

Ok so my boyfriend has kept lizards for about 4 years now .But about a months ago he decided that he would like to give keeping snakes a go . So I said would look in too getting him one for his birthday next month . But I am not sure what type of snake would be best get him as his first one and so would like the opinon of people who have snakes on what is the best kind to have. I would also like to know how much a good snake habitat set up will cost and how much I can expect to pay for a healthy snake and where is best to get one from as I don't want to get one from a pet shop if I can help it. So if anyone help me I would be very greatful.

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