What exactly is a good deal and to who?
When determining a reasonable price for a little rubber figure, a couple scenarios come automatic. One could remember some of the original Monster In My Pocket or MUSCLE packages and splitting up the price among the figures. A ten dollar set of five figures would make you assume each figure was two dollars a piece. Another would bring up their origin of being gumball machine figures, and may only suggest something resembling that.
I, however, think neither of these are fitting anymore. Not only are things like MIMP and MUSCLE turning into niche collector markets, it's become an art platform for all sorts of new artists and toy makers. These new throwback art pieces are neither made in mass quantities or with sub-par materials to cut cost. Independent toy makers pour their souls into these tiny creations, turning cheap slug-mold figures into an amazingly done miniature sculpture.
So now we enter the realm of how much should a piece of art go for, and really, the answer of that is going to be different from one collector to the next. Some people may love one piece and willing to pay anything for it and some won't even pay a dime. That's just how art works, and really, it's going to hinge on whether it attracts the customer on some personal or aesthetic level. The people who get hooked are going to be those who say, no matter what price, that a particular drop or release will be a bargain and a must have. I remember I was that exact way for the Onion Fights X Punk Drunker miniature last February that was being sold for fifteen US. Honestly, that figure could have been twice that and I would have not thought twice about still buying it, that is, if I didn't completely get wrapped up in something else and miss it completely.
Just now, keshi are being released and sold for thirty or so. Believe it or not, that's probably the average price on these Japanese convention-only releases, and some collectors wouldn't think twice. Some people will be hooked onto what a figure looks like or what set it's a part of and will be compelled while other stare and scratch their heads, wondering how anyone could pay anything more than a couple bucks.
Not all things are limited edition and from talented independent artists. You may see some big box superstore carry a minifigure line and wonder what would be reasonable to pay, but I suggest not much changes. Keep in mind quality and materials used, and gauge the price against your interest. I know for me, if something is cheap enough, I really can't refuse.