Your banking cost will typically be 1,000€ - 5,000€ a year with most banks that accept off-shore accounts. You can go with non-reputable banks but you will likely have problems when trying to withdraw the funds.
The fee that you mention of 2500 SCR is for on-shore companies, if you want an off-shore IBC in
Seychelles, the government fee is around 400$ - 600$. Nobody can register directly with the registrar, you need to have a local agent that is responsible for keeping track of the shareholders of your company, the directors etc. This local agent will charge you 1,000$ + the government fee if its a serious agent.
I would highly discourage you from going to cheap providers as it frequently happens that they go bankrupt and there are countless court cases of local agents forging signatures etc.