Rechargeable batteries are quite simply an expensive raw cost. Look up lithium ion batteries---the cheapest one I just found for aftermarket sale in a quick search just now is $71. If you consider that rechargeable battery your baseline cost, then you still have to add the motor, the vibrator itself, the time put into the design, and the silicone cover... it's going to be expensive.
Personally, if I was looking for a quality vibrator but had to skimp on price, I would get a hygenic, waterproof, easy-to-clean and still powerful vibe which took regular batteries (or plugged in, as somebody else suggested, but I like insertable toys better than clit toys so corded power probably isn't going to be for me). Try out the SinFIVE line like the Vuali
, which is only $52 today (and usually $70), or the Evolved Roulette line like Bet on Black
, which is $60 regularly, and often on sale for just under $50.
So you can drop between $50-$100 in price if you don't insist on having a rechargeable product. If cost is bringing you down, maybe choose to be happy with AA's. You can always use rechargeable AA's, too.