Budget Flight sim hardware questions

Okay, I enjoy reading with envy all about all the new processors, video cards mega-mixer machines that get 3.4 million frames per second.... 
But I'm not there. I'm in the low end of the FlightSimHardwareUsers club. I'm a comfortable mile from the cutting edge of hardware. I currently have an AMD Athlon 1700 (1,100) with an ATI 9800 something or other video card, 128 mem. My motherboard is some Biostar or other, don't really care. 1 gig of memory.
I run FS9 with fairly high settings and get frames in the low twenties, or teens with cloud draw extended farther out.
I'm considering an upgrade.
Without spending all my children's inheritance, I intend to upgrade only just enough to barely run FSX, maybe. But my hope is to for sure max out FS9.
I'm comfortable building, but when I start adding up prices, I find I can buy an older system for less money than building one from scratch.
Questions: Best budget processor? I've had zero problems with AMD's, and wouldn't mind staying with them, but I"m open to Pentiums. What is the best line of AMD cores? What is the best line of P cores? How bad are Celerons, really?
Would it be better to keep the video card and get the most processor I can afford, or go ahead and move to a better PCIe card with associated Mobo, and less processor?
How cheap can it be done?
I guess I'm looking for absolute best bang/buck ratio.

But I'm not there. I'm in the low end of the FlightSimHardwareUsers club. I'm a comfortable mile from the cutting edge of hardware. I currently have an AMD Athlon 1700 (1,100) with an ATI 9800 something or other video card, 128 mem. My motherboard is some Biostar or other, don't really care. 1 gig of memory.
I run FS9 with fairly high settings and get frames in the low twenties, or teens with cloud draw extended farther out.
I'm considering an upgrade.
Without spending all my children's inheritance, I intend to upgrade only just enough to barely run FSX, maybe. But my hope is to for sure max out FS9.
I'm comfortable building, but when I start adding up prices, I find I can buy an older system for less money than building one from scratch.
Questions: Best budget processor? I've had zero problems with AMD's, and wouldn't mind staying with them, but I"m open to Pentiums. What is the best line of AMD cores? What is the best line of P cores? How bad are Celerons, really?
Would it be better to keep the video card and get the most processor I can afford, or go ahead and move to a better PCIe card with associated Mobo, and less processor?
How cheap can it be done?
I guess I'm looking for absolute best bang/buck ratio.