Approx. $250 is affordable right now with no problem. With a child, that could be a little more difficult. I'd guess if we'd have a second child, the DVC would be just about paid off. We will take a look at this soon and see what we come up with.
I've worked in health insurance / employee benefits most of my life and here are a few other things that you should factor in:
Health Insurance: Whether you and your spouse are both on single policies thru your respective employers or on one policy together, chances are your monthly costs will increase after the first birth. If you are both on single policies, one of you will have to upgrade to a two party or family policy. If you're already on a two party you'll have to go up to a family. The days of companies offering just "Single" and "Family" rates are mostly over, so you are almost certain to end up paying more as you add a dependent.
The good news is that once you have children 2, 3, 4, etc. there may not be any additional bump.
Birth costs: Depending upon your benefit plan, you may have significant bills just for the birth of the child. HMO-style plans may have just a single inpatient hospital copay to cover the entire birth. But if your plan has a deductible and coinsurance, your out-of-pocket responsibility could easily be over a thousand dollars.
You will also be making regular Dr. office visits for several months (for both the mother and child) so that could add up.
Time off work: This is a tricky one and hard to predict. If it's a difficult pregnancy, the mother could be put on bedrest several weeks or months before the actual due date. Any complications with circulation, feet problems, back problems, etc and the doctor will require that she not work until after the baby is born. Even under the best cases you need to plan on the mother being off work for 4 weeks. If it's a C-section (major surgery) it will be 6-8 weeks.
Having vacation / personal / sick time to cover that time off is best-case scenario. She'll get full pay for the days missed. In lieu of that, find out if she has any Short Term Disability benefits thru her employer. STD often doesn't pay the full wage (1/2 to 2/3 is common), so even while covered by STD she won't be earning her full wage.
Some employers will also require that the employee pay the full price of benefits while on any sort of leave. Most employers pick up a portion (often substantial portion) of the actual cost for benefits like health insurance, life insurance and STD. These plans normally have an "actively at work" clause which stipulates that the employer contribution only applies when the employee is working. For the month or two on STD, she could be subject to paying the entire cost of her benefits.
On the plus side, the IRS gives some fairly decent tax cuts for children. You'll get to claim another deduction and there is also a flat child tax credit which comes right off of your bottom line tax liability. I think the tax credit is up to $1000 per child. Effectively, that's about $80 per month that you can add back into your budget.
Having Grandma willing to babysit will be a big help, and potentially a big money saver. But don't forget to consider some of the worst-case scenarios. Is she really willing to take the child 40+ hours / week so that you both can continue to work full time? If not, can one of you afford to work part time? What other arrangements might you have to make (i.e. day care part of the week) and what will that cost? What will you do with the child when grandma wants to go out of town for a few days or when she's sick?
Back to DVC, if you're planning to buy resale it will help in terms of selling the contract if necessary. However, if you use a broker to sell the contract plan on paying 10-12% commission on the transaction. That's money well spent given the complexities involved, but it will impact your net returns. If you spend $12,000 for a contract now and have to sell in a year for roughly the same price, you could end up pocketing only $10,500 or so. Given that you are financing part of the purchase (and paying interest), you'll probably have to hold the contract for 3-4 years to really break even. And plan on it taking a few months to sell the contract. Over that time you will have to continue making payments on both the loan and annual dues.
Good luck in your research!!!