If you're going to bleach them do it professionally (you might already be planning this, just be aware that stay at home bleach kits, while cheaper than going to the dentist, can be seriously damaging to the teeth!)
From what I've heard, you only have to get your teeth professionally whitened about once every two years, so whilst it can be expensive they stay white for a long time!
However, there are quite a lot of other teeth whintening methods that aren't are no where near as effective but are much cheaper and easier!
Examples include:
whitening toothpaste and mouthwash - there are loads of different brands of this, some with better results than others, so check out online reviews!
baking soda - putting this on your normal toothpaste or making a paste with water or lemon juice and brushing your teeth is an instant white boost, but should only be done on alternate days to prevent the enamel being worn away, and if you use lemon juice maybe only once a week due to the acidity
strawberries - rubbing sliced strawberries on your teeth, with or without baking soda, whitens your teeth by a shade or two, but again should not be done too often!
gels and trays - whitening trays can sometime whiten teeth by 5-7 shades, but needs to be done once every two weeks or so and takes about 30-60 minutes each application - although they are relatively inexpensive they can require a fair amount of effort!
I guess you really need to weigh up how badly your teeth need whitening and how much it bothers you - do you drink a lot of tea/coffee? If so this could be what is staining your teeth, so cutting back on those drinks might not improve the whiteness but will prevent it from getting worse.
I reckon it probably is a good investment if you can afford it/really worry about your teeth a lot.
Hope this helps!