You can buy it used on Amazon, through one of their sellers, several of them are good, and for less than $50. I've also found it on ebay for under $20 not long ago (just depends on when you look) from a powerseller with a 98% possitive and a rating over 400.
Anyway, chance that dragon quest will see a PSN release is nil. It's current state is owned by Heartbeat, Armor Project, Bird Studio, Sugiyama, and then SE (publishing rights only, they own NOTHING else, not the enemies, not the names, not the story, not the game engine). So this requires everyone who owns a piece of it to agree to a PSN release. Heartbeat and Enix never fully settled on their suit (at least in terms of reusing the engine, but they did agree on an out of court settlement for apparent unpaid earnings).
Hori, who basically controls the direction of every project (probably more out of respect than anything else, and because he owns both the name and the rights to every scenario and story through his studio...and because he created the series by having the idea for the game and organizing the joining of the three creators), has stated numerous times that he will never release a port. He doesn't believe in it.
Even if a game seems like a port, it has to be redone from scratch with changes, and enough changes to make for a different experience (DQIV is really the only example with this, read up on the PSX release and the Heartbeat issue if you want to know more) even if that experience is slight, from the original.
Maybe they might do a PSN release, but if they do, it'll be a remake, and the PS3 would have to be the most popular system to be considered for that (in a way, this keeps Dragon Quest sales high regardless of what system they go to, and it really helps promote that system in the waning years in Japan). We're more likely to create a super massive black hole in the middle of Los Angeles that somehow DOESN'T rip the world apart or suck it in, than to see any PSN release of any DQ.
www.backloggery.com/sleeper_hits - Where the good games are remembered. Life can be as much about satisfaction as the act of living it.