Unless you are using a low pressure PCP air rifle, it is best to ditch the 3000 PSI aluminum SCUBA tank idea and get a 4500 PSI SCBA tank. There is also the size and weight issue if carrying around an air tank for refills in the field. I am a certified diver and I once used 3300/3000 PSI SCUBA tanks. The local dive shop in Billings could only fill tanks to 3000 PSI, so I gave up the idea of getting a 4500 PSI SCBA tank from AoA and just went with a 250 BAR FX three stage hand pump instead. In your case, I would go with one of the small compressors made to refill PCP rifles and the small bottles and tanks that airgunners use. The FX hand pump has served me well for 11 years, I have only had to replace one o-ring and clean out the moisture trap, and if I want to get involved with handling tanks I will probably go with a high pressure nitrogen setup. My rifle charges to 3400 PSI/232 BAR, so a standard aluminum cylinder is worthless and if getting into high power PCP air rifles you will eventually have to get a 4500 PSI/300 BAR setup for maximum shot count and maximum power. A person getting an Air Venturi Avenger will need a 300 BAR charging setup for versatility, and if charging from a tank then the tank pressure will need to be considerably higher than 300 BAR, or just get a 300 BAR hand pump. If charging from a cheap used 3000 PSI SCUBA tank, there are better PCP rifles to get than an Air Venturi Avenger. Since you are a Newbie, you seem to have not realized that a 3000 PSI tank and an Air Venturi Avenger is far from a match made in heaven as far as a beginner setup goes. Just get a 300 BAR hand pump for now if cost is an issue, or consider getting another rifle to start out on. What you get is your business, but as for myself I would never consider what you are considering.
When I was starting out, I called up AoA and ended up with an outfit that was matched properly and fit my purposes, which was shooting prairie dogs at long range and hunting varmints larger than bunny rabbits like skunks and porcupines. I ended up with my BSA Lonestar .25 and the FX hand pump. BTW, the salesman at AoA used the same BSA Lonestar for PD hunting in Arizona, so he knew what worked and he had a good number of other high quality PCP rifles he could have chosen from the AoA sales inventory, at higher prices, and he did not try to oversell me into getting something like a Daystate Huntsman Classic, which would have worked almost as well, but at a considerably higher price.
If a Newbie would call up AoA and explain what was needed and what could be afforded, in all likelihood you would get a best buy at that price point. I have dealt with AoA for 11 years and never gotten any bad advice, and intend to deal with them again in the future. They have a sterling reputation to protect, so they are not going to suggest anything that is against your best interests.
