Scott's Specialized US Catalog lists prices for First Day Covers (FDCs) as well as plate blocks.
$1.50 (Scott Specialized Catalog of US Stamps 2011, page 405(First Day Covers))
$1.25 - This stamp Scott Catalog #1756 (1978). First Day Covers catalog for $1.25. (Scott Specialized Catalog for Stamps 2011, page 398)
Scott Number US 1801You can consult a specialized US Stamp Catalog that lists First Day Covers in it. You can purchase the FDC for $2.25 from most dealers.
Yes
First Day Covers: $1.50 (page 393)This stamp isn't worth a lot. It is Scott Catalog #1003. Issued as a commemorative issue Dec. 10, 1951. 116,130,000 million were printed (page 529). There are 5 values for this stamp and they are:New: 20 centsUsed: 20 centsFace: 3 centsDealer: 4 centsSheet: $11.50 (Brookman Catalog)(Scott Specialized Catalog of US Stamps 2001, page 101)
There wasn't any Lincoln First Day in 1952. The nearest to that was in 1954. The catalog value of a 1954 FDC is $1.50
That would be US Scott Number 2417. A First Day Cover has a catalog value of $4.
Scott Number 1359. Catalog value is $2.95.
Not a great deal. The First Day Covers with the gold replicas are available for less than $4.
The 2009 Scott Specialized Catalogue of United States Stamps & Covers puts a catalog value of $2.25 on the W.C. Handy stamp issued in 1969. (No one is likely to offer you as much as catalog value.) You can see one offered for sale for $2.91 at http://stampstore.org/sto_displayItem.asp?StampID=106360088
Commercially produced First Day Covers of standard commemoratives like this are typically worth about a dollar. The Bicentennial stamps may bring a slightly higher value. Higher value stamps, or specific cachet makers are worth more. A specialized catalog will list the value of a cachet or un-cacheted cover.
Commercially produced First Day Covers of standard commemoratives like this are typically worth a couple of bucks. A complete set of the 50 states will probably cost around a $100. So a dealer would purchase for a portion of that. A specialized catalog will list the value of a cachet or un-cacheted cover.