I’d say three tips you can look into are the Final E, Spiral Dots, or AZLA SednaEarfit XELASTEC tips. First two are my personal favorite and really comfy. The Azla are kind of weird taking in and out but not as bad as foam tips. They are really comfortable once you have them in your ear since it conforms to your ear.
Your budget is great to work with! I am not sure how possible it is to get the sound of the Nanna 2.0 even if there was a custom Nanna 2.0. So keep in mind, whatever IEM you choose, it will sound different than the Nanna 2.0 even if you hear the universal counter part. My impression from reading reviews of it are they are a really smooth sounding U-shaped sound signature while still being a bit engaging.
Best advice I can give you is to try and listen to the universal counter part first or a universal demo of the custom. For example, for 64 audio A12t, try and see if you can demo the A12t universal rather than the U12t. U12t sounds similar, but A12t does sound a bit different. This is coming from someone who has/had 3 customs and blind bought two of them. Even the one I didn’t blind buy, the custom sounded different than the universal. Audio shows like CanJam or RMAF are happening this fall so if you can wait, those would be great to attend to and will save you from having regrets on your investment on a custom.
Since I haven’t heard the Nanna 2.0 personally, hard for me to gauge on what IEMs can match its tuning. I have the Elysium universal and has the best mids I have ever heard on a headphone or IEM. It’s so good. I enjoyed it for modern pop for sure. It has an engaging tuning to it with great mid range timbre, but it’s a bit more of a specialized IEM. Can’t comment on how good it is with jazz or classical. BA bass may not be as good for rock. Can potentially pair alright with a neutral source like the M11, but really really shines with something like the Shanling M8 which is a warmer highly technical source. It’s a try before you buy kind of IEM, but if you really like it, you’ll love it. MusicTeck offers auditions so you can email them to see if you can try them out for a couple days assuming you live in the US.
I used to own the U12t. Has a really smooth and coherent all rounder signature. “Boring” in a great way. Kind of IEM with high amount of technicalities and the music disappears making it easy to do work in. APEX modules are really nice for long sessions. A12t takes the smooth signature and makes it a bit warmer. I imagine it’ll be a bit less musically engaging as the Nanna 2.0, but is great if you’re after an all rounder where you want to do work in or want the music to disappear in the background. Or want to relax. Z Reviews who raves about the Nanna 2.0 also raves about the U12t.
I haven’t heard the FiR M5, but based on reviews, that could be a great option for you as well.
Edit: Even though U12t has BA drivers for the low end, it has the best bass from BA drivers that I have heard. Not quite as good as some great dynamic drivers, but it is better than some dynamic drivers.