80€ for Makita and 40€ for no-name brand. They've been tested and the 5Ah rating is accurate. What's remains to be seen is how these last long term.
A friend has his own electrical business, he buys unbranded batteries for all his DeWalt kit and claims never having an issue. He also says the higher capacity ones are really good.
That said there are dodgy ones out there. Buy from a reputable seller.