Thank you Trail!
I'll do my humble best to offer some suggestions that actually are within your stated budget or at least not wildly over it.
As I am sure you know, 2-3K rounds per year is not "High volume" by any stretch of the imagination. Its about what I shoot. So the truth is that any decent quality gun that meets your other requirements......cast on, monte carlo, O/U, under $1200 (or close...
) will do the job.
Naturally, my suggestions are prejudiced by my own experiences.
1) Always my sentimental favorite. DeHaan. O/U, cast on, left hand top lever, 28 or 30" barrels, custom stock dimensions, Monte Carlo stock, 5 choke tubes, grade III wood, choice of 3 engraving patterns. $1,600.
Yes....It's a Huglu. And it is over your stated budget, but it is the best bargain in the left hand world. The cast on and leftie top lever should make your son very comfortable and truly encourage his interest in the shooting sports. At the rate your son shoots it will last him well into the point where he is making enough money to pay for the next step up himself. The guns are made to order and you'll have 6-8 months to pay for it which should help with the 33% "over budget".
2) Call Chuck at TR Imports and see if he has any O/U, cast on guns with monte carlo. He is offering a 10% discount until the end of the month so total cost would probably be $1,000 or less. Again....a Huglu, but at 2-3K shells per year that is not an issue.
3) Can you find a Neutral cast gun that fits the other requirements (Monte Carlo, O/U) that runs $1050 or less? If so, get it and send it to Mike Orlen and for $150 or less (including R/T shipping) he will bend the stock to cast on. Can he bend a cast off stock to cast on? I don't know. Call him and ask. Does good stock bending, offers discounts to SGW people, works quickly.
4) I'm running out of ideas. But Mike Orlen's services should open up some possibilities to you that would bring some other guns within reach of your budget.
5) You don't have to buy used or spend $2,000 or more to get your Son a gun that will serve him very well for the next 10 years or so at the rate he shoots.
Happy hunting! Get the boy a gun that really turns him on and help built the next generation of shooters!