Unless you have a very strong and concrete reason for preferring MS Office, I suggest Open Office as a replacement. It’s free, while MS Office costs the price of a computer.
My advice is don’t be stingy but don’t cross your limits. For example if you see an 80 GB hard drive for $20 less than a 120 GB hard drive, don’t save the 20 bucks. Just make sure you get a good bargain and you aren’t making unreasonable savings. Similarly, it doesn’t make that much point buying a twice slower graphics card for a dozen bucks or two difference. Even if you don’t seem to need it, it’s just a bad idea to make small savings of cash at the expense of big differences in hardware properties.

For example see that the numbers calculate well and remain in proportion - hard drive capacity to cash, graphics card benchmark score to cash, processor parameters/benchmark to cash. These ratios make a good purchase.

If this sounds like Chinese, I can help you out.
Generally, if you tell me how much you want to spend and what company you want to buy from, I could help you make some choices.
Note: If you really only ever intend to do office works, it may be a good idea to buy a used computer from a friend or some company which is doing away with post-leasing computers or some such
and also use Open Office (which comes for free) to save the most cash and get the best results at the best price.