The best "budget" planar even now: second hand Audeze iSine 10 (or if you can find a B-stock one) with the Cipher cable (which makes it iOS only). The Cipher V1 cable (much rarer) has excellent tonal balance and the Cipher V2 is more V-shaped but still technically great. Both have the best staging/imaging under $1000 (along with the iSine 20) and the bass is pretty good. Issue is: these are open-back for the most part and has zero isolation. Also they are very uncomfortable. I bought two of them and sold both so yeah despite having some good stuff I don't find any use for them. However, if you can deal with the fit - they are as good a planar IEM as any (with the Cipher cable, stock tuning is awful).
Not necessarily, since Audeze has a closed back iSine and those sound decent (though very expensive). But making closed-back headphones in general is more challenging than open-backs and in case of IEMs the enclosure is very small so not much room to
diffuse the resonances etc. Also, small planar diaphragms in general don't sound any better than a competent dynamic driver or BA driver array. They are more novel than really good at anything in the sound department.