You shouldn't have to convince a customer, once you have explained why you have gone the route you have that should be enough.
You don't need the customer who buys on price only, they will be nothing but a pain in the arse. I give a price and that's it, you know straight away whether or not they are interested.

As to regards holding up, only time can tell. I have a small Techno Isel router, no idea what it cost new and it's only 300 x 300 working area but it's been a very good machine for me.
Is it well made ? So so, never gave trouble other than having to strip down to lubricate but it could have been made a lot better, supported rails etc but it is robust.

Looking at it you can see ways of improving it. Then looking at the 6040 other than possibly better stepper mountings / bearings and supported rails on the Y axis [ although some say they have them ? ] it looks a good design.

Then look at a Heitz <sp> machine and for what you get for the price I think these are total junk but a lot of users swear by them.