Shopify Create a custom app

We are not a shopify plus store. We need to allow partial payment (10%) payment option for the customer (instead of customer paying the full price). I already have a project posted to achieve this, but this is 2nd project to see if someone can do this for me. What you need to do is create a new custom app. This app will be shown as an added payment option in the checkout page. The only purpose of this app is to take the current total amount of all products in checkout page, and get 10% of that total and send it to our normal credit card gateway. For example: all product total in the shopping cart checkout page is $100. Then customer will see 3 payment options in checkout page:- 1) Pay via credit card ( this is the current option to pay in full) 2) Pay via paypal (the paypal button already in checkout page) 3) Pay 10% down payment (this is the alternative payment method that you will have to make) If the customer select option 3, then his order total for 10% is paid via our current credit card payment gateway (bambora) which is already installed Do not make bids unless you have read the project description. Only make bid if you can do this and have understood all requirements We are looking for someone skilled in Shopify to do the following:- 1) enable a partial payment option for the customer. This is how it should work: We have a shopify site (not shopify plus). We have over 3000 products, all different prices. We want to do the following:- 1) In product page, show 2 options to the customer:- a) first option is the current default Full payment option b) 2nd option which you have to make is 10% payment option (which is equal to 10% of the product price) 2) If the customer selects the first option, then everything works as per normal as it is full payment option 3) if the customer selects the 2nd option, then the following things should happen a) in the checkout page, the product price that customer should pay should be 10% of product full price b) in the checkout pages, There should be a new line added to Product title: "Layaway Order" This is very simple project, but I understand that shopify does not allow to modify checkout page for Non Shopify Plus Stores. So you have to design it such, that if customer selects Partial payment (2nd option), the product price and product title should be modified while sending to checkout page I need a very skill and reliable shopify expert for this. I will not give you access to my site. You have to create a test site first by yourself and show me your code is working, then i will give you access to my site to move the code I have already tried other shopify available apps, and they do not meet my requirements. So do not suggest that i use one of those apps.