Getting Price and Add to Cart Button. Any thoughts on what I am doing wrong

Question

I am trying to get the price and add to cart link for a product

This is what I am testing at the moment, is it completely wrong?

========== Setting Variables ===========

{% set giftDepositID = 6901 %}
{% set giftDepositPrices = 0 %}

{% if craft.commerce.products.id(giftDepositID)|length %}
    {% set giftDepositproduct = craft.commerce.products.id(giftDepositID).find() %}
    {% set giftDepositvariant = giftDepositproduct.defaultVariant %}
    {% set giftDepositpurchasableId = giftDepositvariant.purchasableId %}
    {% set giftDepositPrices = craft.childsown.getVariantPrice(giftDepositpurchasableId) %}
{%endif%}

========== Example HTML ===========

            <div class="col-xs-12 mobile-price-item">
                    <div class="row">
                    <div class="col-xs-12">
                        <img src="{{baseUrl}}/assets/images/softie-robot.jpg" class="img-responsive">
                    </div>
                </div>
                <div class="clearfix bg-gradient-yellow">
                    <div class="col-xs-8">
                        <h3 class="text-gloria">{{"Deposit"|t}}</h3>
                    </div>
                    <div class="col-xs-4">
                        <h1 class="text-white text-gloria"><span class="initprice" data-usd="{{giftDepositPrices}}">${{giftDepositPrices}}</span></h1>
                    </div>
                </div>
                <div class="row">
                    <div class="col-xs-12">
                        <form method="POST">
                            <input type="hidden" name="action" value="commerce/cart/updateCart">
                            <input type="hidden" name="redirect" value="commerce/cart">
                            <input type="hidden" name="qty" value="1">
                            <input type="hidden" name="purchasableId" value="{{giftDepositpurchasableId}}">
                            <button class="form-control btn btn-yellow text-white" type="submit" data-click=".softie-form .red .btn">{{"BUY NOW"|t}} <i class="fa fa-play"></i></button>
                        </form>
                    </div>
                </div>
            </div>

Any help/guidance is appreciated.

======= EDIT ========

New Variable set, I have updated the following:

{% set giftDepositID = 6901 %}
{% set giftDepositPrices = 0 %}
{% set giftStandardID = 6899 %}
{% set giftStandardPrices = 0 %}
{% set giftLargeID = 6897 %}
{% set giftLargePrices = 0 %}

{% if craft.commerce.products.id(giftDepositID)|length %}
    {% set giftDepositproduct = craft.commerce.products.id(giftDepositID).find() %}
    {% set giftDepositvariant = giftDepositproduct.defaultVariant %}
    {% set giftDepositpurchasableId = giftDepositvariant.purchasableId %}
    {% set giftDepositPrices = giftDepositvariant.getVariantPrice(giftDepositpurchasableId) %}
{%endif%}

This is the output of the HTML

<div class="col-sm-4 pad-sm red">
<img src="https://childsown.com/assets/images/softie-alien.jpg" class="img-responsive">
<div class="block-container">
<h3 class="text-gloria">Deposit</h3>
<div class="block">
<h1 class="text-white text-gloria"><span class="initprice" data-usd="">$</span></h1>
</div>
</div>
<form method="POST">
<input type="hidden" name="action" value="commerce/cart/updateCart">
<input type="hidden" name="redirect" value="commerce/cart">
<input type="hidden" name="qty" value="1">
<input type="hidden" name="purchasableId" value="">
<button class="form-control btn btn-red text-white" type="submit" data-click=".softie-form .red .btn">BUY NOW <i class="fa fa-play"></i></button>
</form>
</div>

Answer 1

I am a little confused with your twig code assigning so many variables.

Put simply, only a purchasableId can be used to add something to the cart.

If you know the product ID then it is as simple as:

{% set product = craft.commerce.products.id(6901}.first() %}

{% if product %}
    <form method="POST">
        <input type="hidden" name="action" value="commerce/cart/updateCart">
        <input type="hidden" name="redirect" value="commerce/cart">
        <input type="hidden" name="qty" value="1">
        <input type="hidden" name="purchasableId" value="{{ product.defaultVariant.purchasableId }}">

        <button type="submit">BUY NOW {{ product.defaultPrice|commerceCurrency }}</button>
    </form>
{% endif %}