Hi there,
Thank you for your question. I do believe we are the only ones with this app for sale. Our price is $50 per month as can be evidenced by visiting our website at: http://gold-feed.com/shopify-gold-price-live-app.php . If you would like to pay yearly I can create you a manual invoice. Our application is integrated with Shopify's billing API so it is preferable you use that so that Shopify gets their commission.
Regarding the different markup for higher quantity buyers you would use another app in conjunction with ours. Something like: https://apps.shopify.com/quantity-breaks
Thank you for your question. If you have anymore inquiries please do not hesitate to ask.
Regards,
The Gold Feed Inc Team.