Long story short I'm quite confused as to exactly what is offered by domain registration and dns service sites.

When I go to the url "http://google.com", my PC connects to a name server and gets the IP for "google.com", then connects to the IP and says, give me the page for "http://google.com". AFAIK there are many name servers and they all cache these bits of information in some hierarchical network, but ultimately a DNS record must come from a single source (not sure what this is called). There are different kinds of records, that might not an IP but an alias/redirect to other records for example.

Lets say I want my own domain name for some server. Maybe it even has a static IP but I want a nicer thing for people to remember, or my ISP assigns dynamic IPs and I want a URL that always works, or my website is hosted on a shared machine so the browser needs to send "http://mydnsname.com" to the webserver to distinguish it from other requests to the same IP but for different sites.

Registering a domain costs a small amount of money per year. Where does this money go, not that I'm complaining :P? Is that really all it costs to maintain the entire DNS system of nameservers? If I just register the domain and nothing else, what do I get? Is that just reserving a name or hosting WHOIS information or have I paid for a dns recrord to be hosted? Can a domain alone have a record, such as an IP or be an alias to another?

A bunch of sites out there offer other services, in addition to domain registration (I'm assuming they register the domain through another party for me). One example is "dynamic DNS" (DDNS), but isn't this just a regular DNS record that's updated regularly? Does it cost extra to update more often? Without a DDNS, can a DNS record still point to an IP? I've also seen the term "managed DNS" and have no idea where that fits in.