How much would you charge to build a complete ZATCA Phase 1 & Phase 2 e-Invoicing solution?

I'm trying to understand the market rate for developing a complete SaaS/web-based ZATCA-compliant e-Invoicing platform for Saudi Arabia and would appreciate estimates from agencies or developers who have experience with similar projects. The scope would include: Core Invoicing Create, edit, delete invoices Tax invoices and simplified tax invoices Credit notes Debit notes Proforma invoices Multi-currency support VAT calculations Invoice templates PDF generation QR code generation ZATCA Phase 1 (Generation) Fully compliant invoice format TLV QR code generation Arabic and English invoice support Required invoice fields and validations Printable invoice formats ZATCA Phase 2 (Integration) Integration with ZATCA APIs Compliance CSID onboarding Production CSID onboarding Invoice cryptographic stamping Invoice hashing Digital signatures XML generation according to ZATCA specifications Clearance invoices workflow Reporting invoices workflow Automatic invoice submission Real-time status tracking Error handling and retry mechanisms Certificate management and renewal Business Management Customer management Supplier management Product/service catalog Categories Units of measure VAT configurations Branch management Company profile management User & Security Multi-user access Role-based permissions Activity logs Audit trails Two-factor authentication API access for third-party integrations Reporting & Analytics Sales reports VAT reports Invoice status reports ZATCA submission reports Export to Excel/PDF Dashboard analytics Additional Features SaaS architecture Multi-tenant support REST API Webhooks Email invoice delivery WhatsApp sharing Backup and recovery Localization (Arabic/English) Responsive web application Cloud deployment Technical Requirements Modern web stack Secure architecture Scalable for thousands of invoices per day Production-ready deployment Documentation For agencies that have built ZATCA solutions before: What would you charge for a project like this? How many