Build three separate pots
Start with recurring costs: accommodation, utilities where applicable, food, local transport and communication. Put travel to the destination, initial transfers and any necessary equipment into a second pot. Keep a third reserve for changes. A refundable deposit still needs cash up front; do not treat it as money available for everyday spending.
Compare the same arrangement
For each room, record the full term, total price, included utilities, cleaning, internet and payment schedule. Ask whether the quoted rate assumes a commitment longer than you want. Compare the total for your actual dates, not an attractive monthly figure beside a different minimum stay. Check the local rules that apply to the accommodation before paying.
An illustrative month
Imagine 1,000 currency units for accommodation, 450 for food, 100 for transport, 60 for communication and 190 for other recurring items. That is 1,800 units. A 15% reserve adds 270, giving 2,070. Add arrival costs separately. These deliberately neutral units demonstrate the method; they are not current prices for a specific city.
Track an ordinary week
Use a simple record with date, category and amount. Distinguish one-off exploring from habits you will repeat. A week of arrival meals and sightseeing is not a reliable sample of a settled month. Adjust the plan after you understand your routine rather than treating the first estimate as a promise.
Keep rules outside the arithmetic
A budget does not establish permission to reside or work. Resolve those questions using the relevant official authorities and qualified advice for your circumstances. Then price a stay that is permitted, including any confirmed administrative costs.