Yeah..buy a used xr50 for $900 and when your kid outgrows it sell it for $850...3k? We're talking 50's still right? Msrp for a NEW pw50 is $1300 and a ttr50 is $1850. Buy one that's 2 years old for a few hundred less and sell it in a couple years for $200 less. Or buy a cheap Chinese one for whatever they cost and throw it in the scrap pile or if you're lucky get $300.
And get parts from your local Honda dealer (in the unlikelt event you need anything other than a spark plug) within a few days rather than weeks or possibly never. Oh and there's the fact of mechanics refusing to work on chinese junk so you'll need to know what you're doing (if you can get a part this month )