Is it possible to get an original DEC pdp-7, if so how much would it be? I've looked around the internet, but I'm not finding anything.
PDP-8 and PDP-11 machines seem to be much more available. The Living Computers museum in Seattle has a PDP-7, which may be running: it would be worth asking them if you could have a login for it.
To buy one, start haunting eBay. Price would be unpredictable, and probably quite high for something in running order.
In short: no.
A well-researched list of PDP-7s sold and their fates is available here from soemtron.org. There were approximately 50 PDP-7s manufactured, of which only 4 are still known to exist. They're all in museums.