That's a pretty broad question. In some cases, yes an AU58 may even be worth more than MS60 bid, in some cases no. It depends on the individual coin, date & mm. It also depends on the buyer since some 58 coins are way nicer than some 60's. And in some cases, even Grey Sheet bid or ask can be totally meaningless for any grade.
The bid is what a dealer is offering to pay for a given coin of a given grade. The ask is what a dealer is asking to be paid for a given coin of a given grade.
No. Here's an example - let's say I want to buy a Morgan dollar. And I offer to pay $75 for that Morgan dollar - that's the bid. Then I find a dealer who has the Morgan dollar I want - he wants $85 - that's the ask. I can either accept his ask or decline it - and he, like me - can either accept my bid or decline it. Or the two of us can agree on a comprise and I can pay him $80 and we're both happy.
Relys a lot on eye appeal which is very subjective and hard to quantify, but quite often an AU58 can have better eye appeal than an MS-60 (or even 61 or 62). Some AU58's have good eye appeal, original luster, maybe some light toning, little or no contact marks, but because they have a trace of wear they don't qualify for an MS grade. A coin with any wear at all can't grade higher than AU58, but can still have great eye appeal otherwise, and can actually be more desirable (and thus demand a better price) than some MS60's or even some as high as MS-64. Depends on the coin, and on the buyer.
I really like the look [and frequently the price] of EF to AU coins compared to their uncirculated counterparts, which frequently seem grossly overpriced to me. But I figure I'd take a beating on a resale someday since it seems that only uncirculated coins are desirable by a majority of collectors unless they are key dates or otherwise scarce. I guess EF and AU coins are mainly for collectors who don't care about resale value.
