They probably don't count as 'affordable' being about $70 each, but my best gf bought me two of the Glamourmom bfing singlets from Babies Galore (or similar). They might be a little more pricey, but they lasted me for three years (and have now been put away for number two) and were so versatile (wear on their own in summer or under a shirt when it got colder) that they were worth every penny. I had some other styles that also worked (aippers up the side, for eg), but the singlets were by far the best. I would go out and buy them at that price before spending a lot less on something that needs replacing or doesn't do the job.

They were also supportive enough for me to not have to wear a maternity bra under them (after the first couple of months). You'd have to try them on to see if that would work for you, though.