I'm sure Ryanair would like to be able to fly to Lappeenranta promoting it as a proxy for St Petersburg.
The big issue for a LCC, is that most people living in West Europe need a visa for Russia, which is likely to put off a good proportion of people wanting to visit. Don't get me wrong - I've applied for countless visas for independent travel in the past from countries which really don't like having foreigners talking too their citizens and know that for Russia there is a well-trodden path to getting the paperwork, but it all adds hassle and cost when the rest of Europe is visa-free.
A while ago, there was talk of tourists from the EU being able to get a visa on arrival with minimal paperwork. Did this come to anything ?