To elaborate on what YoshL mentioned about some of the pads:
StepmaniaX Stage (SMX pad)
StepmaniaX Stages started as $1,337 each. Now they're $1,360 and can be expected to increase to approximately $1,385 when you take into account a yearly 2% inflation rate. Shipping is also high (for me it was $275). This means you'd actually aim towards spending roughly $1,650 for one of them if you go with the shipping option as opposed to local pickup.*
*Reason why I started with the shipping method as opposed to other options listed like local pickup is due to the insanely high demand where you battle time vs. buying the pad. Because the demand was so high, the pads sold out within 3 minutes of the link going live for the 100 units that were available in early August this year. You can expect something similar to happen in the next wave. People have expressed concern about locking a purchase request once the user is brought to the order details screen so they don't have to rush in the order.
Something else to consider about SMX is that it is highly supported by the original manufacturer. There is a
central store you can go to for most of your needs: whether it is sensors, riser frames to push up your center panel for more level panels, etc. There is also a software configuration tool to check your pad's sensitivity in real time when you are adjusting it. All in all, it's a great pad but the price is definitely up there and every wave could take anywhere from 4-6 months at the current rate. I'm not sure entirely what the bottleneck is, but this is currently the case.
Precision Dance Pad (PDP)
I got one of these originally, and if you're planning on playing songs mostly below 180 BPM and below the 13 ITG level range, these are okay. But when it comes to higher level play, they don't fair very well -- I can agree with YoshL that if you're seriously going to be into the game, these are not the best option. When I got mine it was $350.
Impulse Platforms
The rumored price for an individual Impulse Platform pad was in the range of $600-$800. This means you could potentially get one for nearly half the price of one StepmaniaX Stage, also using sensors based on load cell technology.
As YoshL mentioned, there have not been any units available for Impulse Platforms yet. It's not clear when they will be releasing the first wave of pads, and the lack of transparency as to what the roadmap is (e.g. next two months planning on testing, then release early 2019) is what is turning some people away from this pad as an option despite the positive feedback about the prototype.