Combined with the models I already have (that came with Assault on Black Reach) I have decided to create the army in two stages,
Stage 1, Space Marine Battleforce.
Games Workshops 40k Battleforce boxed sets (and their Warhammer equivalent) are very good value and the Space Marine is no exception. It provides a nice helping of Troop options to make sure I will have models able to take and hold objectives and a Rhino transport to make sure they can get there fast! The Assault Marines would become Vanguard Veterans to give them better stats and an edge in assault over other Elite units.
Stage 2 Specialist Units.
The first stage only really gives me a Space Marine army, this is deliberate. By learning how to fight with a basic Marine force I should be all the better prepared to drop some specialist Blood Angels units into my force. These first units being Death Company (of course!) and a Baal Predator. These units should give my force a more Blood Angels feel and give the enemy five blood crazed lunatics heading for their HQ units and a nasty shooty and FAST tank to worry about!
This should give me a cost effective and flexible 1500 point Blood Angels force.