If your fiance is planning on coming here to get engaged and stay and marry that is fraud for him to come in on a visitor visa.
You need to file a fiance visa for him. To to that you must have had a face to face meeting within the past 2 years.
The I-129F will cost $340 plus a $350 fee for the visa processing fee. After she enters the U.S., then you have to marry and then you have to pay $1070 for the I-485
Unfortunately, you will have to be patient because it will take a total of 6-10 months for you and she to go through the arduous process of her immigrating.
You will file form I-129F with the USCIS here in the US at the lockbox (PO Box) as per the instructions.
You must include with the form a G-325A for you and she along with 2 passport style photos of each of you.
You can find those forms and instructions at this link
Once your petition is approved (it will take 3-5 months) you will be notified and the petition will be sent to the National Visa Center. In approximately 2-3 weeks they will send you a notice and instructions for her to begin the visa process by submitting the DS-160 & 156K Visa Application.
After that is received the USCIS will request her background/security check be done by the FBI she will then receive her instructions for her medical and visa appointment.
She will be told what documentation to bring.
She should document your relationship with pictures, cards, emails, printouts of your skype conversations, etc.
You also need to discuss your personal life details in detail such as where you work, physical address, your position, job duties, details about your family and details about them, such as where your children go to school, work or other information about them if you had a family previously. You should converse as much as possible in English as it is best for her to do her interview in English as that is additional evidence of you having a good relationship - that you can communicate in a common language (unless you are fluent in Spanish).
After her interview she will be told to leave her passport and the immigrant visa packet will to sent back to her within 2 weeks at which time she may travel to the US. She has 4 months to use the visa.
Here is a great link to a flowchart with timelines