Expert needed: Fix Shopify Product Variant Logic

We are facing critical issues with the variant handling logic in our Shopify theme for products with multiple variants. The current JavaScript implementation only works reliably for single-variant products and fails to consistently detect the selected variant once multiple option combinations are involved. This results in incorrect availability states, broken “Add to Cart” or “Make a Request” button behavior, and malfunctioning notify-me app integrations that rely on accurate variant data.

After changing options, the UI often does not update correctly even when a valid variant combination exists.

To resolve this, the existing variant logic must be analyzed and rebuilt so that the currently selected variant is reliably detected on every change and all related UI elements update immediately. This includes availability, price display, button state, and integration events for third-party apps.

Additionally, we use a price-based button switch where variants above 1,000 € display a “Make a Request” button. This logic currently runs only once on page load and must be updated to react dynamically to variant changes by checking the price of the selected variant each time.

The solution must be clean, maintainable, and future-proof, without temporary fixes or workarounds. Strong Shopify theme and JavaScript expertise is required. Please provide a fixed-price offer, your proposed budget, and a brief outline of your technical approach.

Please check everything and tell me budget and time