Sendgrid Integration

I have a single pager website with one form subscription. I have following things done till now. When user subscribes, he gets email for joining. And after 3 days he should get email for sharing the website. Above things are handled via sendmail for time being but I wish to get sendgrid integrated in place of sendmail. Cron is already written for 3 days schedule. I need it live today, so whoever bids, should be available for work for next 1-2 hours (as sendgrid integration wont take more than an hour). The bid is for sendgrid integration. API is available on github and person who is good in PHP should have no truoble doing it.