comments:
There IS a 6" dob that fits into a 40cm x 30cm x 18cm box https://a.co/d/0bXzk8Kp No reason the same concept cannot apply to an 8" Or there is also a binocular made from TWO 8" mirrors that fits into a 56cm x 36cm x 23cm box. https://www.analogsky.co/bloom I am not quite sure you can build one for about the cost of a 10" however...
I believe they meant to post this link https://a.co/d/0g2hrb8p Handydob, a 6" dob that fits into a suitcase. The only downside the price. But it is still within your budget and since you want portability, you have to be willing to pay for the portability, so it is still a good option.
How about this? Ed Ting loved it, it seems very high quality. Nearly small enough to count as a personal item let alone carry-on.
Speaking of a portable 6" dob, this might be a great suggestion. https://a.co/d/003xbSbl