As a fellow left-hander I can say the ultimate solution is just to learn to shoot right handed. Being able to switch hands is great for looking around cover anyway. There are a fair few holsters you can't buy left handed, but most of the genuine ones you can.
If that's not ideal though, then I'd look to eBay - obviously spend what you can afford to, but there are plenty of good vests out there by Tactical Tailor, Flyye and many others. I run an TT MAV and also own one of the tactical vests too. Both are pretty excellent. Don't buy new with only £30-40 to spend on a vest, because it'll likely be pretty naff.
For the holster: Maybe a Blackhawk Serpa clone with a molle adapter. Going to set you back approximately £20 in total if you order from broad, and most of the clones are alright in quality. The other option is a Warrior Assault Systems universal holster - they do that left handed too and they're set for almost any pistol so have that going for them as well. Those don't often go second hand so you're looking at about £28.
