Playing Online DnD 5e using both Roll20 and Beyond what to buy in each place....

Im roleplaying strictly online nowadays as GM and I have been scratching my head on how going about it with DnD5e since both roll20 and beyond have their purposes but buying every book in both can get pretty expensive (ex. Descent into AVernus bought in both platforms sums 70US$+ almost). Since I dont have the time to homebrew much these days im going to run published scenarios mostly so im guessing i may just buy core manuals and sourcebooks on beyond for better referencing options and campaigns and scenarios on roll20, since the real problem using Beyond material is to properly import maps from Beyond that match the grid for correct lighting, plus having npc and monsters already on the VTT is a nice plus. Referencing rules and other stuff is much better in beyond. Of course the easiest and best solution is to buy everything if you have the money, but i think I came to a good middle ground. Thoughts?

Buying published modules on Roll20 makes most sense. Can't say what might be best for you when it comes to the rest, but sounds like you had a pretty good idea for yourself.

Charactermancer is awesome and the more source books you have the more options in the  Charactermancer. I own The core books and then buy the modules I want to play. My players pitch in to help pay for the books but we have been playing as a group for over 20 years. I have been there GM for 5 years. The only thing I don't like is that you can only use the books with Roll 20. A PDF of the book should be included in you purchase. The only thing we get from D&D Beyond is special things like one of the players wanted to play Echo Knight so he purchased the rules for it for $1.99 I think then you can just add the info to the character sheet.  

Yeah I agree that the Charmancer is amazing, and have everything on Roll20, even use it for creating characters I've played offline, which I've then transcribed to paper. It's a pity though that the UA and Elemental Evil Players Companion isn't on Roll20 & the charmancer/compendium, would be great if it existed as a separate compendium you could turn on/off alongside your other compendiums/SRD compendium. Just noticed that Customize Origin is possible in the Charactermancer, don't think we had that very long?

if all your players are also on beyond, that platform is excellent, and I would rather use that. I would only buy the Modules here for the prebuilt maps and tokens that are included. I would get the rest on Beyond, with their highest tier.

I'm doing the same thing - I much  prefer DDB for content and character sheets, and so I use that for my players with the Beyond20 extension for making rolls on Roll20.  I've purchased all my sourcebooks and adventures on DDB, and then repurchased the adventure modules on Roll20 as needed, which is expensive, but for me it's worth it to not have to set up the maps and tokens and dynamic lighting.  Also, I've found that some of the player maps on DDB are not great -- for example the PC version of Icespire Hold from DoIP shows all of the secret passages; but those maps are typically fixed for Roll20, because things like secret doors are added as images on the GM layer. One thing I see infrequently is asking the entire group you're playing with the share in all of the costs.  It certainly happens, (I think it happens more often than is talked about online) and when you do the math D&D can be a fairly cheap hobby if the costs are shared.  Let's say you want to go more than just the basics and get 5 sourcebooks (PHB, DMG, MM, XGtE, & TCoE) at $30 each ($150), plus some adventures for $50-$100, along with the DDB Master Tier ($60) and Roll20 Pro subscription ($100), that's $350-$400, which is quite a bit for one person to pay out.  But if you are splitting that 5 or 6 ways, you're looking at $60-$80 per person, with only $30-$35 of that recurring annually, and that's assuming you didn't wait until DDB had a sale (they regularly have 10-25% off sales).  Everyone's financial situation is different, but if you're able to get a steady group and play weekly or biweekly, the price per hour is quite good.  And there's also the issue of who 'owns' all the content, because it'll be tied to a specific account, so if you end up having a falling out with a player... it's not simple!  But definitely consider talking to your players about their willingness to share in the costs, and you'll likely be surprised.  

Thank you all for the repllies and advice. While Charactermancer is good(i use it with Call of Cthulhu) I find  the DDB character sheet amazing and the referencing of rules much better. With the Beyond20 extension it can work like a charm with Roll20 VTT.