My opinion is that there are some items in there that are worth digging for , and a handful of small lots , separated , sorted a bit will get you well over your $550.
what you really need is a few things to begin with :
1.) get everything that came from Walmart outside the barn , make a pile. if you are not sure , look for names like "magna " " Next " etc , etc .
if it says a bike shop quality bike name on it .... campagnolo, trek , specialized, fuji , etc goes in the barn.
there are lots of lists online from biking co-op donation sites and from bike buyers of things the WILL NOT ACCEPT ,
its safe to through out pretty much anything stamped Made in china and advisable to keep anything stamped made in taiwan , japan , Europe and USA in the barn
and DO take the white Schwinn traveler , and the roadmaster frame into the barn.
2.) find someone in the family , your church , a friend , or a good doer, a local bike mechanic who knows bikes to help you sort and sift , old ( pre 1980's part and pieces and bikes may have value , as may better best quality when new from 1980's onward )
tell this person you want to preserve / harvest old school stuff, and ID modern era stuff.
if you get such a persons time , line up a third person and yourself to stand by with markers and tags , grocery twist ties to wright what they ID onto labels.
3.) line up a metal scrapper take a pic of the pile and offer him $20 towards gas money to take the pile away.
4.) group and sell off manageable lots. Lots that fit into the likely buyers POV, whatever vehicle they are likely gonna roll up in. each lot should fit into an average car or SUV with some careful breakdown and packing by the buyer and no lot should larger than fits into a full size suv , or pickup truck bed .
5.) tools: your grandpa likely had lots of other types of tools other than bike specific tools. take your time with these and once the family has taken what they want , ask those family folks to ID and price tools.... tools always sell well if you know what it is you have and describe. IF you old clamps , vises or bike specific tools , you ( or your cousin ) are well on the way to $550
once you manage to get the walmart stuff outta there, and if you turn up some sorted (better quality / or vintage ) bikes and parts , do pass along pics and i'm sure you'll find folks here to ID older stuff or current stuff that might be of value. including piles of nuts and bolts if they are bike specific.
Finally , there's an army of guys here that hold onto big piles of bikes and bike stuff.... we all have to face it , sooner or later , our kids and grand kids are gonna have to deal with our pile , realistically , most will chuck it in a dumpster .
But , your grandpa would be honored if you can find time to sort out some of the better / coolest things and get make an effort to get the best reasonable value you can under the circumstances.
good luck!