http://www.dakkadakka.com/dakkaforum/posts/list/69.page JForum - http://www.jforum.net
If it's any help I'm also considering a Necron force]]> http://www.dakkadakka.com/dakkaforum/posts/preList/669502/8238996.page http://www.dakkadakka.com/dakkaforum/posts/preList/669502/8238996.page GMT
For example, Librarians are great low point HQs. Perfect for 500 point games. But in larger lists, you might be using a demi-company, and be locked into a chaplain/captain. Or you might be doing a bike list and have a chapter master riding around smashing things.

Particularly since you mentioned cash, you don’t want to buy something now just to have it warm the shelf later.

Also, how competitive do you want to be?

My generic suggestion for 500 point SM lists is as follows:

Inexpensive HQ (Librarian, Chaplain, or Techmarine; Lib is the strongest option)
Full tac squad (preferably in a transport)
5 man scout squad
Fun unit of choice (You should have a bit over 100 points to field something that excites you)

I think this gives you a small force that captures the feel of a marine force, and does OK on the table.

A more competitive army, but very WS centric, would be a bike HQ, 2 small squads of bikes, and some support option like a TFC.

It might also be worth looking into formations. Not just for what direction to collect/build, but some do fine as low point options by themselves.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/669502/8239253.page http://www.dakkadakka.com/dakkaforum/posts/preList/669502/8239253.page GMT csm. Ideally I'm wanting something that is fun but can hold its own I will probably go with
Librarian
9 man tactical squad with melta Combi Melta Rhino
5 sniper scouts
Thunder fire cannon

Chapter tactics wise I might just go Iron Hands]]> http://www.dakkadakka.com/dakkaforum/posts/preList/669502/8239448.page http://www.dakkadakka.com/dakkaforum/posts/preList/669502/8239448.page GMT