It costs as much as your ID card costs by the government, and lasts as long as well. They are one and the same. Applying for a new ID card / national ID document in Estonia costs 35€ and the document is valid for 5 years. If you forget your PIN code, you can reset it with your PUK codes, but if you also lose your PUK codes you need to apply for a new ID card. The process for getting a new ID card from the moment you applied for it takes no more than 30 days. You can also have it fast tracked for 250€ and get it in 2 days.

But, like the parent said, you have many other options other than the physical ID-card as well. Most people these days use Mobiil-ID or SmartID, which works on your phone and even smart watch. SmartID is completely free and Mobiil-ID is tied to your phones carrier, so the cost varies, but it's a one-time set-up fee of around 5€. Mobiil-ID certificate also lasts 5 years.