birthday/anniversary trip

10 days total? That's not a trip that's a getaway. So forget any plans to cross Asia or see more than one place. It sounds like you are trying to squeeze a backpacker experience into too short a time and frankly it just wont happen.

For an occassion like this you are much better off picking somewhere romantic or somewhere that means somewhere to you (it could be anywhere in the world) and enjoying that place.

For example, Singapore or Hong Kong are fantastic places to explore and small enough to see and relax in for 10 days (including wasted days at the start and end for transit and acclimatisation), or try Bangkok for 5 or 6 days then Kanchanaburi (a few hours away) for some mild elephant trekking, waterfall hiking etc). And you will have a great time in all of these places on that budget.

How to put this nicely. You say nothing about your interests so how do you expect anyone to suggest anywhere? You might as well close your eyes and stick a pin on a world map. For TT posters to list hundreds of places would be a complete waste of time.

For example, if you said you were into hiking, photography and natural scenery I might ask you if you have ever been to the Anza Borrego State Park and the town of Borrego Springs, in southern California. But what would lead me to suggest that given what you have written?

The more relevant info you provide the more relevant responses will be. Otherwise you are just asking us to waste our time listing places of no interest to you whatsover. The TT is not a travel agency.

You sound adventurous people. My first thought was India, which has many possibilities, but June is just too hot to enjoy them.
So how about Ethiopia? Ten days might just give you enough time to see the northern rock-carved churches plus Addis Ababa and maybe some of the Omo Valley (the great continental rift). The weather is temperate all year round there, because of the altitude - though I can't remember if the end of June coincides with one of their two rainy seasons...

Kansas City to Addis Abbaba is around $1500 per person return. That's $3k out of $4k gone. That budget doesn't allow for going any real distances from the US Midwest. Basically, it will take $1k each to leave the continent.