Well namedcheap.com is a parked domain so you would need to do a whois on it and find out when the lease expires. I don't think namedcheap.com will get you in any trouble with namecheap.com. In fact namecheap.com would probably sell you namedcheap.com. As for how much it costs well that is down to however much a .com is with a registrar.
Well the domain namedcheap.com is not too attractive to namecheap.com so you won't have any problems.