The typical 'Russian Romance' scam will involve an initial request for a sum to cover an airline ticket to your destination, visa and permit expenses, and maybe money for a medical examination. Generally the intial amount will be somewhere around $1000-1500, and they'll want you to send it via WESTERN UNION, a favorite method of scammers, worldwide!
Assuming you send the initial amount, and seem willing to part with more, many catastrophes may befall the 'lady' on her way to the airport. She may have an 'accident' on the way to the airport, and need medical expenses. Her luggage and passport my be stolen, and she needs money to replace them.
A parent may be in critical condition in a hospital, and they need a little more money for the 'life saving' procedure or operation.
There are endless 'emergencies' that can be used, and if you're willing to help with expenses, you may be asked to finance a series of them.
How much do you need to throw away before you become suspicious? It's up to you!
Sometimes, 'quick and dirty' scammers will make a rapid 'seduction' and scam for a 'modest' amount, maybe $300 to $500.
I've seen reports of men being repeatedly scammed by the same 'lady', and eventually sending various amounts of money, totalling $5-10,000!
By the way, they never 'met' the lady! You will never meet her, either!
OTHER scams involve you paying for 'translation' or 'agency' fees. Essentially, you're paying hansomely to get some pre-packaged emails and pictures of a pretty girl.
You may be steered toward some other type of 'scam', after intitially being contacted in a 'romance' mode. Nigerian 419 scammers do this, prowling internet dating sites for victims. After a few romantic letters, you could be scammed for travel expenses, or steered into some other fraudulent activity.
Remember, these are criminals you are dealing with. They don't care about you.
They just want your money!