So I did some research and maybe someone could verify if I`m getting this right.

1.My client needs to get a merchant account in a bank.
(this can be done by talking with his bank or using some service
like worldpay.com (the only service I found that has no limitation
on where the business has to be))

2.My client needs to subscribe to a payment gateway service

3.Possibly an online shopping cart service must be used, because payment gateways require HTTPS connection.
(HTTPS is not avaiable in the website in question)

P.S.
My clients business is in Latvia.