my advice:
buy the domainname.com
get to work
make money
dotcom is the beachfront property of the web.
i agree completely with others about visitors to the squatted domain thinking you closed up shop. my very first online company (~1996) was a small .net, i didn't have the $700 to buy the squatted .com, and at least once a week i'd get a cc chargeback because someone placed an order and a couple days later erroneously went to the .com and saw it was squatted, thought i closed up with their money and called their cc to do a chargeback.
occasionally i'd receive a write-up in print media that would foul it up and refer to my website with the .com instead of the .net.
that was the late 90's though, but the concept of their mistake still applies today, whether it be 'word of mouth' traffic, 'trying to remember the domain name' traffic, etc.
it is my opinion that in almost all circumstances, where we are now with the web, and across most every demographic, anything other than domainname.com will just send an amount of free traffic to domainname.com.
you pay for advertising, they get traffic.
as the misdirected traffic rises to a squatted domain, the price will usually go up. as my dotnet ventures soon proved profitable i wished i had bought the dotcom name right from the start. competitors wiser than myself did, or in the better case it was bought by someone in a coincidentally unrelated industry, and i just dealt with the chargebacks and loss of traffic and phone calls asking what the website name was.
from that lesson i've bought squatted dotcoms just because i saw heavy advertising by a competitor on the dotnet or the hyphenated dotcom. nothing better than hitting the ground running.
my experience shows a squatted domain asking $3500 can usually be acquired for $2500, ordinarily i'd offer $2000 maybe $1500 and see what they counter with, but i surely wouldnt let that $2500 offer he made or even $3500 keep me from making money. see if he'll take $2000. the follow up email with the $3500 price may have been a template mail from an inventory management system he uses if he has lots of domains. i wouldn't think he's being snarky since you didnt jump at the $2500. but as soon as he sees someone (you) has the alternative domain name, he's not likely to entertain that $2500 offer anymore, unless he has to make rent.
i currently have about 3500 domains, maybe 75 came from squatters. most of my domains are unhyphenated dotcoms. generally i'll resort to alternatives such as dotnet or hyphens if my only intended source of traffic is an internet search and i'm not concerned with repeat visits.
it took me a while to get past 'the principal' of dealing with squatters. the way i look at it now is that i appreciate the fact that they took the initiative to hold the 'good' domain name for me and keep it out of the hands of my competitors until i was ready to use it. nowadays i pay $1k to $3k regularly for good domains. i stepped up for $20k recently for a squatted domain asking $30k (plus i had to pay a 10% premium to the 'broker'). it's the cost of doing business. it's an investment. be patient, you'll get the money back, and more.
just be glad the squatter who has the name you want is still in the realm of attainability for normal people, and isnt asking $1m or something like that.
i do understand that when just starting out even at half the price buying the domainname.com might simply be out of the question, in which case, i'd recommend the domain-name.com over the domainname.us (even the web super-novice knows what that .com means, no accompanying text required. if i had to use the domainname.us i'd always present it with the www. in front, to help clarify things for the web novice).
as soon as you see that this venture will make money and be around for a long time, and not just be a playtime hobby site, i'd suggest you start saving every penny you can to get the domainname.com domain. doesnt matter if you've invested in print ads for the alternative name, just redirect the traffic. dont worry about a temporary search index hit from moving the domain name, just redirect the traffic properly.
i don't know all the details, but make certain your friend knows you appreciate the opportunity, don't squander it. respect and learn from his experience, wisdom, insight. do not discount what he has learned in business, even if it might predate how business is done on the internet. play your cards right and this could set you up for the rest of your life. i've been right where you are now.
