Tallinn is the priciest of the Estonian cities but still cheap by Nordic standards, and your bed is essentially the whole budget — walking is free and a day's transport costs less than a coffee.
What a day costs
The shape of a lean day: €2 buys a one-hour transport ticket, a weekday fixed-price lunch replaces dinner, and you pay for one indoor sight — attraction entries here run roughly €10–16, with the Energy Discovery Centre at €16 on weekdays and €18 at weekends. Walking the Old Town and the bastion parks costs nothing.
Hostels around Kalamaja and Balti Jaam
The dorms between the station and the wooden-house streets are a five-minute walk from the Old Town and consistently cheaper than beds inside the walls. Prices swing hard with the season — midsummer and the New Year are the peaks.
The €2 hour ticket
Tap a contactless bank card on the validator, or buy a QR ticket in advance; one validation covers an hour on buses, trams and trolleybuses, and you must validate every time you board. Free travel exists but is tied to Estonian benefit documents and pre-school children, not to visitors.
Päevapraad — the weekday lunch plate
Roughly noon to three on weekdays, most Estonian kitchens outside the tourist lanes serve a single fixed main course at a fraction of the evening menu. It is the largest single saving available in the city and it is not advertised in English.
The free half of Tallinn
The Old Town lanes, the bastion parks, Kadriorg's park and the coastal path east towards Pirita all cost nothing, and they add up to a full day. Keep the ticket budget for the two or three indoor collections you actually want.