How fussy are you as a listener?
I would take a budget of 35K, spend about 15K on the HU + speakers, and spend the rest on sound isolation. A second layer of bitumen and under-carpet will cut road noise by 20dB, so you get a lot more detail and even a cheaper system will have a chance to impress.
I find the biggest problem in car audio today is how much sound from outside gets in and how much from inside gets out.
That said, it is possible to spend your entire budget on just the HU.
You should spend more money on speakers at the sitting location (if you drive yourself, better speakers in the front). All HUs will cap out at 17 watts a channel, no matter if they say 40 or 50 or whatever dumb figure. Some can struggle up to 25 watts at reasonable quality, but if you want more power, then an amp is the way to go. Even a very basic 4-channel Sony amp will do about 35 watts a channel, which is much more suitable for music.
If you want to fit the HU, amp and all speakers into that 35K budget, they'll be all mid-to-entry level stuff (there's nothing wrong with that BTW, in spite of all my apparent snobbery my car system is a very basic Sony HU and 4-speaker setup, and that too wired out of whack 'cause I don't have the time to go get it fixed).
Just so you know, prices abroad may not necessarily better, but you may get a wider range to choose from. Most stuff available here is just as cheap, plus Rockford/Fosgate etc are available as long as you know where to look.
6x9 is a no-no for me. Round speakers are the only way to go, too many problems in the midrange. For only bass they might be OK but those are very badly designed. Components wherever possible, a good amp, and good wiring are the key. Those things push the bill up very quickly.
