Your model 4 knife is probably 1963-5 or so, the sheath probably being '61-'62 or so.
Here are some equivalents to your 60s model 4 for sale on E-bay. These model 4s, 7s, etc. all have brown button sheaths and are more or less time equivalent to your knife package, '60-'65 time span.
I would ignore the knife that has a "buy it now" price for $1500. Many people have outdated expectations. The first two are the ones I think most important for comparison of ASKING price to your knife. You also may find it more up to date and useful to watch the last one as it is active bidding.
Model 4-5, 1960-61,
$785
http://www.ebay.com/itm/Vintage-US-C...4AAOSwRLZT84v7
Vintage Model 4-5, early 62-63 ?
asking $810
http://www.ebay.com/itm/Vintage-1960...IAAMXQrC9ScSZR
Model 7-4.5, about 1962,
asking $1,500
http://www.ebay.com/itm/antique-Rand...IAAOSwyQtVw9os
Vintage Model 7-4.5, Late 50s (?) Heiser, ?
current bid $405, five days left.
http://www.ebay.com/itm/Vintage-Anti...kAAOSwzgRWuqjM
Below are two model 1s that may be more or less equivalent. Actually both may be a bit older and have some additional desirable features... but they should give you an idea of what people are ASKING for model 1s like yours.
Model 1 ? early ?70s, 7-spacer, features ?
asking $825
http://www.ebay.com/itm/Randall-Knif...MAAOSwQYZWwJsU
Model 1 ? 1970s
asking $855
http://www.ebay.com/itm/US-1970s-Cus...oAAOxyf1dTHfqK
This next one is much more collectable, knife is good, sheath rough, issues, but you can get some idea of what is being asked.
Model 1-7, early 1950s, Koren war-Vietnam, cornrow heiser sheath.
$800
http://www.ebay.com/itm/U-S-Randall-...3D252300109239
There are many others on ebay if you search for "Randall knife 1." However, some are wildly overpriced, some have lots of desirable or collectable features, and some are con jobs. The key is to find ones in your general time period and condition. The ones above are the ones that appeared useful to try to bracket current price. Keep in mind your model 1 is not necessarily from a collectable time period, though it is indeed older. My advice is to be modest in your expectations.