I actually like the idea of Crobat+Virbank City Gym for 60 damage from poison between turns. This list seems kind of clunky, though, and looks like it would get slowed down by lots of different lines and high-energy, fairly lightweight attackers.
My first suggestion would be to drop the Metagross line. Getting everything working with any Stage 2 line is tough right now (especially without Tropical Beach) and adding a second is kind of a logistical nightmare.
The problem with Giratina is that it takes lots of energy and isn't always useful. In fact, if the Defending Pokemon is poisoned, it probably has been since Crobat attacked it last turn. That means it's taken at least 120 damage (40 from the attack itself plus 40 from poison between turns), and if Virbank City Gym is in play, 160. Any Pokemon with 160 damage on it doesn't need a 3-energy attacker to knock it out.
I would also focus more on just Crobat. Beef it up to a 4-3-4 line and take out the Snorlax and a couple (or all of the) Giratina. Giratina seems like a bit of an energy suck for the damage it's doing; you really want to focus on Crobat here. For extra Basics, Deoxys EX seems like the way to go to add more damage and provide a bit of a secondary attacker, but if you're on a budget that might not be possible (at least until the Deoxys EX tins come out). If you do go with Deoxys, I would run 4 instead of the 2-2 Garbodor line in the list below and replace the Silver Bangles with a Silver Mirror and 2 consistency cards.
Mew EX would be a possibility as an easier-to-set-up attacker. I also really like the idea of Garbodor DEX here (without Mr. Mime, of course) since you'll be running tools anyways to deal with Crobat's low HP. Of course, Crobat's Ability is actually pretty nice to have, but shutting off Abilities isn't so bad. You can always choose to not set Garbodor up if it would hurt you. I can understand why you'd veer away from Garbodor, and there are certainly other options, but it's not too bad if you're staring down a Plasma deck and don't want your Crobats to keep being one-shotted. I would not run just a Crobat line, though. It adds room, certainly, but running only 4 Basics is a bad idea in terms of allowing your opponent to get set up faster and see large chunks of your deck in the process. 6 is iffy.
You kind of need Super Rod, what with a Stage 2 130HP main attacker. I've added in two to compensate for that as well as the slightly low energy count below.
Silver Mirror helps a LOT against Plasma decks and Silver Bangle helps against EXs. You do 40 with Crobat, add 60 between turns (Crobat makes poison do 40, then Virbank adds 20 more), then 60 before it comes around to your turn again, and that's 160 damage. With Bangle, that's upped to 190, which means if you can get an EX stuck active (which is a big if), it's better than a OHKO. If not, you still can do 130 damage before it rolls around to their turn.
You need Ultra Ball. If the entire Crobat line were Team Plasma, that would be so nice, but unfortunately, that's only Crobat.
With all these Pokemon and such, it's hard to find room for Supporters. There are 10 in the list below, but a lot of lines are thin. 4 Catcher is ideal, 3/3 Bangle/Mirror would be much better, another Rare Candy would help, etc. I've forgone Hypnotoxic Laser; it doesn't help with consistency and if this deck works, it has to work because of Crobat, not HTL, which isn't sustainable.
This list is something I just made, so obviously it isn't close to perfect. But it's more where I would go with this deck. You're on a budget and some of these cards are somewhat expensive (and who likes buying individual cards anyways?), but I'd recommend at least simplifying your list, beefing up the Trainer line, and focusing more directly on Crobat and Virbank City Gym.
Pokemon (15)
4-3-4 Crobat
2-2 Garbodor
Trainers (33)
4 Professor Juniper
4 N
2 Colress
3 Colress Machine
3 Pokemon Catcher
3 Silver Bangle
2 Silver Mirror
3 Rare Candy
3 Ultra Ball
2 Super Rod
1 Computer Search
3 Virbank City Gym
Energy (12)
4 Plasma Energy
4 DCE
4 Psychic Energy