I have a Japanese pachislo machine. They're fun for parties or when you have friends over, but I never play the one I have on my bar on my own. It's for show more than anything, because it lights up and makes a lot of noise. Plus the attract screen is cool when nobody is playing it. But that's about it. I had two before, but I sold one to a guy for helping me with some bathroom construction work, and I never missed it at all.
The older original American slot machines will run you a lot of money; figure between $750 - $2000 for some of them. Pachislos are Asian, and much, much cheaper. You can pick one up for around $200-$350 (avg). If you're talking newer games you can only play in casinos right now, good luck. Those can cost many thousands of dollars. Your best investment is a Pachislo right now. It is entertaining and has an affordable entry price. You can find them used for under $200 easy.