Being one of the lucky few to get my Steam Frame a few weeks ago, I have been using it quite a bit since then. I have been buying some third-party accessories to mitigate some of its weaknesses.
First the obvious one: it is surprisingly light and small, but overall not comfortable enough due to my glasses. To solve that I went ahead and bought prescription lenses from VR Optician (119€ including fast shipping and additional prescription fee).
Then I figured I had better protect it against sunlight because I do not have one of those fancy head mounts nor do I want to pack it in its box between each use. Thus I got an AMVR lens cover that fits quite well (13€).
And finally the battery life situation is... Well it's bad. I got decent VR legs and can play for hours, but the battery only lasts at most 1h30 when running PCVR at 120Hz. So I got myself a UGREEN Nexode 145W 25000mAh Power Bank (56€), 2 short angled USB-C cables (24€), round magnetic USB-C adapters (16€) and a small fanny pack (10€).
I will also say there has been some trial and error regarding the magnetic adapter. The idea is to protect the headset port in case the cable snags on anything. I wanted to plug it directly in the headset port, but it tends to disconnect when I turn my head. The tradeoff I landed on is : one very short cable plugged in, magnetically coupled with a longer one that goes to the battery. The 240W-rated USB-C cables are also overkill but hey, not that much of a price difference (they are quite thick though and contributed some in my disconnect issue).
So there you have it, 238€ on top of the initial Steam Frame + ergonomic accessories kit purchase (which is a must-have if you ask me), not counting said trial and error.
Update: there are strong arguments in comments against using magnetic adapters. I'll be ditching that and keeping the 2 cables approach so that there is a straight connection (hopefully weaker than the angled plugs) that can unplug more easily than the battery or headset side if the cable snags on something.
I don't think you can call it "true cost" because you purchased some accessories.
However I do agree that there are accessories missing that I would call mandatory. A battery pack being one of them. It seems Valve prioritized weight and comfort over longevity, which is probably a fair compromise. But you really do need some sort of external power.
I ordered the other UGreen battery pack with 20% less capacity but 50% less price (45W).
And I'm still waiting for 3rd party accessories comparable to the "ergonomic accessory kit" like the hand straps that absolutely should have been included for like $10 extra and not $60.
I thought that title sounded better than "Here are all the thingies I bought to go along with the Frame" 😇
The ergo kit is indeed pricey but I doubt you can get that low. Somewhere in the 20-30 range would have been more reasonable. I am not sure I understand why they made the top strap optional at all. Plus coming from the Index, the controller straps feel more natural.
I haven't felt the need for a top strap, personally. Plus it would mess up my hair :( but I've seen lots of people saying that should be mandatory included as well. Seems like Valve was really trying to get the price as low as humanly possible without compromising the hardware itself. I am glad they left out the charger though, as I've already got a drawer full of them, including 2 Valve ones I never even opened...
I had heard from reviews that the top strap was basically not needed. Then I tried it for myself. What it does is alleviate the pressure on your cheekbones as the headset no longer sags and allows you to loosen the horizontal strap a little, also lessening the overall pressure on your face.
It is not needed in the sense that the headset is wearable and has that "ski mask" look without it. I for one will never be taking it off.
I haven't noticed any pressure there, but of course everyone's bone structure is different, which is part of what makes VR headsets so hard to make!
I did read some info online in the months before receiving mine and many people suggested moving the rear further up on the head, which might alleviate that pressure.