Frankly, for most purposes, "close enough" really is close enough. If you are doing critical work it's usually for a good enough reason to make the cost of something like a Lacie Blue Eye monitor/calibration system just a part of the cost of doing business -- it'll pay for itself before too long. Or at least you'd be maintaining some hope that it will.
For most hobby purposes, as long as there's a reasonable match between what you're seeing on-screen and on paper (no major surprises, like purple blues or orange reds, nothing is much darker or brighter -- you'll want to be close enough that it'll take some looking back and forth and hemming and hawing before you see really, really minor differences) you're good to go. You may not be able to satisfy an art director with a book of Pantone swatches clasped firmly in hand, but that was never the aim, was it? Most consumer monitors only cover the majority of the aRGB color space, and they're perfectly adequate for all but the fussiest work.
Your Samsung, though it is getting long in the tooth, supports 24-bit color (which is more than a lot of low-end LCD monitors really support these days). The contrast is a little bit low (critical calibration may not like it) and is probably lower now than when it was new, but it should be adequate for most work -- habituation will take care of the dynamic range (um, I mean your eyes will adjust). If you can see the difference between 255,255,255 and 254,254,254 and between 0,0,0 and 1,1,1 (put a square of one in the middle of a square of the other -- you may not be able to actually tell the colors apart, but you should be able to see the edges) then you've got enough to work with.
The IBMs, though, are probably not up to the task. IBM has made some amazingly good imaging monitors, but they're not the sort of thing that ended up in a cubicle farm very often -- they usually wound up in medical imaging departments. Still, if you can empirically prove them to be "close enough", then they are probably close enough. You never know -- you may have stumbled across a pair of the good ones.
If you are thinking about going pro, then those minor differences start to count. (You'll probably want to chose somewhere other than Costco for your printing as well.) You can start with a more sophisticated monitor calibration, like the Spyder 3 system. A wide-gamut monitor wouldn't be a waste of money either. If you're shooting advertising, then trading your car for a Lacie 30" setup might actually be worth it. But unless you are what they (tongue in cheek) call a "well-heeled amateur", there's no sense spending money where you don't have to.
