sending download links on auto after paypal payment

Hi all ive been a lurker for some time this is my first post im selling stuff through ebay and it seems to picking up pace as the more listings im adding =more sales as they are digital items im at the point of all items loaded up on google drive & copy paste the link in a message to the buyer i know it doesn't seem like a problem now but at the rate its going it will be in a month or 2 once theres 1500+ items
ive looked at e-junkie sounds a good idea but most of my items are 200mb - 1gb so its not going to take many to fill up their largest plan and become costly.
what i need is something that can recognise which of the many items have been bought via the paypal notification and in turn will forward the appropriate link to the buyer?
ive gotta think forward on this ive already got a domain & host to put up soon but i cant jump between the 2 for the next month or so as neither will get my complete attention (imagine juggling all that and still manually sending links) has any one got any ideas or pointers im not the sharpest at the techy side so if the youngster working with me cant crack it il buy a bit help in.