Build this tool: Bridal/Service Business Day-Rate Calculator

For bridal hair/makeup, mobile pet grooming, mobile detailing, and similar
service-based creator businesses: enter travel time + travel rate, on-site
hours + hourly rate, product/materials cost, other overhead, and desired
margin — get a suggested day rate with a full cost breakdown and effective
hourly rate. Live-updates as you type.

Product folder name: Bridal-Service Business Day-Rate Calculator
Difficulty: Easy
Category: People & Blogs / Creator business
No Gemini — pure arithmetic.

STACK (standalone desktop app)
- Python 3 + tkinter GUI — standalone desktop tool (not a website).
- Even if an idea brief says "web app" / "site", ship a Python desktop GUI for v1.
- Include: main .py, requirements.txt, run_*.bat, build_exe.bat (PyInstaller), exports/ folder.
- Smoke-test core logic offline without requiring live API keys when possible.