To keep it cheap, I recommend
1 Lord Commissar (use your Commissar model)
1 Platoon Command Squad with Vox Caster
2 Infantry Teams with Vox Casters and Lascannons
50 man Conscript blob
Aegis Defence Line with Quad Gun
That comes in at 555 points. Now do as follows:
1) Set up the Aegis Defence Line in a U shape, the front facing the enemy, as close as you can get
2) Quad Gun in the front middle of the wall, Lord Commissar in base contact, hidden well behind it
3) Along each arm of the wall, run the infantry teams up in rows of two. Lasguns should be towards the front, followed by Lascannon, and then Sergeant and Vox
4) Fill in the rest with your 50 Conscripts
5) Platoon Command Squad go up the back
So you have a Ld10 blob of guardsmen, all with a 4+ save, able to fire at anything within 48'' and turn it to dust. Order your Conscripts each turn to First Rank Second Rank.
Also, as you have a Platoon, any Vendettas you get can carry an additional Guardsman Team, I recommend Plasma Gun and Pistol. One of those will come in at 210 points. A squadron probably won't help, but if it's what you what, there is nothing stopping you.
Also for extra fun, Guard and Angels can share psychic powers, so if you take Divination on the Librarian you can have all types of fun with the Guardsmen.
Yes, this tactic falls apart under barrage and ignores cover weapons, and blast weapons will ruin your day. This gentlemen is why you must target these weapons first.
Hope that helps