I know that but like are you locked into the shipping ootion you choose or they give you prices for all shipping options and give you the option to swap to the cheapest one.

You're not locked exactly, but you can't just switch at checkout like you can on Amiami. You'll have to email them to ask to change the shipping method and even then, you won't know how much the cost is until after they've implemented the change.

What I do is, I find those items or something close- comparable in size and weight- on Sahra and see how much it would cost for a particular option, and expect a +/- of ~2500Y on that estimate just to be safe.

Ok so im only looking for one item, the sentai artisan digitaizer and battle raizer set. Im trying to get it from nakano or any of the 3 stores that have it. Sahra has it as well. But the estinate that Sahra gives, thats their final price for shipping?

In the case of just that particular item, yes. It changes depending on how large/heavy the overall parcel is, so if you're getting multiple items it's subject to change.

But here's the estimate on the store page (Sahra):
https://i.imgur.com/CCRXcCW.png

And here's the quote when I take it to checkout (Sahra):
https://i.imgur.com/HAvxPBX.png

So this would be about what you could expect to pay at Nakano or elsewhere, give or take 1000 yen or so.

Can the price change drastically if i add say 3 rider shikishis, 3 ranger keys, 4 keychains, and a yugioh promo booster pack? Cause with these using sahra to check, it keeps jumping between 4400 yen and 6300 yen

Assuming all of that is fairly flat it probably wouldn't be a substantial increase, if any. If you start adding Figuarts or similar, then you can expect a bump before too long.

So it could jusy ge sahra glitching and overcharging? And yeah all of it is small and flat. Much smaller than the artisan box.

I can't say for certain, again, it depends on how big the overall parcel is and how heavy. A few ounces can make a huge difference.

anyone ever use a site called Ukiyo Kumo?

Huh, never heard of it, will check it out