In short: Keep package inclusions, personal spending and contingency separate.
Audit the quoted inclusions
Check meals, airport transfers, station transfers, luggage, seat choices and any local visits you expect. An excluded service is not necessarily unfair; the issue is whether it has been allowed for in your budget. Ask for the total payable amount rather than calculating from an advertisement alone.
Match every included service to a person and date. Breakfast for two adults does not necessarily cover a family, and a transfer at one end does not imply a transfer at both ends.
Allow for everyday spending
Create separate lines for meals outside the hotel, laundry, local transport, connectivity and shopping. These are planning allowances, not fixed charges. Use your own habits and current quotations. Someone who returns to the hotel for meals will budget differently from someone who eats out every day.
Check arrival and departure times against hotel access. If an early arrival means you need a room before standard check-in, ask what arrangement is possible and what it costs. Do the same for a late flight after checkout.
Make contingency visible
Add a buffer for changes and unexpected purchases, but do not use it to hide known costs. Review the budget in one currency and record the exchange rate date if converting. The calculator on this site uses SAR inputs and your own figures; it does not fetch live prices.