You're in the process of designing the house?? So nothing has actually been built yet, right??
And the situation is that you want a well-built house as inexpensively as possible. So there are two main things you can do - alter the design of the house and/or do some of the labor yourself.
In terms of design - the more 'square' (or 'rectangular'), the better. Every bumpout costs money and it makes the foundation more complicated.
Simple rooflines are better - the cheapest (and probably the best in terms of stability/longevity) would be a gable roof. Complicated rooflines are expensive to build and are more prone to leaks. Dormers add significant cost.
Two-story houses are cheaper to build than a one-story house (same square footage).
Keep water lines close to each other. Keep bathrooms either next to each other or above one another. If they're close to the kitchen, that's even better.
Plan for the future. If you think you might need more room in the future, plan to add on later. We're not just talking about having more children - do you have any parents that might need a place to stay, etc. Maybe pitch the roof higher to leave room for future expension. (Yes I know it's a bit more expensive - but it's a heck of a lot cheaper to finish off an attic than to build an entirely new wing.)
Think 'multiple use'. Don't design rooms for specific uses, you'll probably regret it in the future.
If you want 'well-built' - well, would you consider buying an older house and fixing it up?? I bought a fifty-year-old house and had it moved to my property. It is so much better built than the current houses (which are built like
[email protected], IMHO). And much much cheaper.
Does your builder have any 'stock' houses that you like?? If he's already built a dozen houses of a certain design, he'll be better (and faster) at it than if he has to build one he's never done before.
I would reconsider omitting the walk-out basement. That's relatively cheap space that might come in very handy in the future. Think about it.
The work you're talking of doing (finish painting, etc.) is definitely do-able - but remember that this is what you 'see' and makes a big difference in the appearance of a house.
Look for bargains in the newspaper. I just bought (two days ago), over 4,000 square feet of 3/4" thick, 3" wide, tongue-and-groove pine paneling for $1,500. That's about 1/7th the cost of the local Lowe's or Home Depot. I found a new $900 sink in a thrift store for $35.00. I bought doors through ads in the paper.
Remember the old saying - "You can have it cheap, fast or well-done. Pick two out of three". If you're in a hurry, you'll have to choose between cheap and well-done.