Attaining or buying only Maps and Assets of official Adventures?

Hey, I'm fairly new to Roll20 and DnD in general. After playing for soem months I also wanted to be the GM for a short campaign to see how it goes. I like having hardcopys of thigns and I also want to be able to play offline so I  of course bought my basic book offline. Yesterday I also bought the DnD starterset to take my first GM steps. But now I am wondering, do I really have to buy the compelte adventure again if I want to play it on roll 20 aswell with friends I can't meet easily? or is their a way were, since I have the adventure next to me, obtain the maps and assets or at least buy only those for a few bucks? I would be very disappointed If I ahd to buy the complete adventure again..... Thanks in advance for any info!

Mike Schley is the map contributor for the starter set. He sells them on his site, and it looks like the price for the Starter Set is down to $10.  That said, most of the adventure maps' cost is high, but there are sales here and there, and there are no other assets, unless you buy from Roll20 in this case. It's often more cost effective to buy the adventure, where available, from your platform of choice's provider because of the digital map cost. Roll20 seems to be adding the newest adventures, but nothing else as yet (Older adventures and Monster Manual, for example). You can expect the price for the assets to match MSRP. 

Thanks for the reply :) I had hoped buying the physical adventure would somehow prevent me from paying for it again online but I guess I'll have to improve my drawing skills ^^'

It's not only the maps you are paying for, its the work that has been put into it, the maps are all set up with dynamic lighting, all the monster tokens have been fully stated and the tokens themselves made, the entire campaign book is also provided, with a bunch of other stuff. And 10$ is nothing to pay for something like this :)

Also true^^  And yeah 10 bucks isn't really much^^