Hi Charlie, I think you've just opened the flood gates for a million software providers to get in touch with you! So without further ado, here's the quick(ish) sales pitch from my company.
Agriya were the first company to develop a ready made daily deals / group buying platform back in 2009. Since then we've sold the software to businesses on every continent, around 40-50 different countries.
I'm not sure what programming language your developers can work with, but our software is programmed in PHP and uses the CakePHP 2.0 framework which is very well documented on cakephp.org - it uses an MVC structure to aid development too.
As far as I'm aware, all the software companies that have a ready made solution are based in India which will bring its own set of advantages and disadvantages. Prices range from $250 up to over $3000 just for the software. Agriya's software is priced at $1,000 and you get lifetime updates and 3 months of technical support.
Agriya is an 11 year old web development company, has nearly 200 full time employees including 5 CRM's and 15 technical support staff. Please check out facebook page http://www.facebook.com/agriyanews where we post updates about the company and general Internet news.