I would need it to run 2 sicce pumps, 2gen 3 radions, skimmers, 2 gfo reactors, one dosing pump, 2 mp10s total, 1 maxspect gyre 130, 2 uv sterilizers, and a few random things that I cant think of at the momment
are you looking to run only the tanks? or would you want to run some stuff in your home as well? harbor freight has inexpensive ones that would be good for just your tank, but for afew bucks more not bad investment depending on where you live and frequency you would need it for. I bought a generac year or so ago, thankfully I haven't needed it for more than starting up to make sure it runs
Figure out the wattage you will need and then buy one that is sized well over the wattage you are using.
Also, with the equipment we use I would suggest a inverter/ generator which are going to go against your "cheap" interest. If you don't buy a inverter/ generator you could easily fry sensitive equipment.
Buy that General 8000 for sale on here, it's a good price and more than enough for what you need. Also I'm pretty sure that one can convert to turn on as soon as you lose power. I would double check on that, but most generacs at that size have that option. You would need extra parts and an electrician to do that though.
Personally I would recommend a Generac Rapid start 5500, which retails for about $ 659, but you can likely buy from a local Generac dealer for less. Try to track down a Generac dealer/electrician in your area, as they can get you a better price on the unit and install anything you want to add on. I purchased a 5500 last year, and had an electrician hook it up with Generac's new transfer switch. The 5500 is powerful enough to run my 300 gallon reef, and a variety of things within my home. While this may be over-kill for what you want, the Generac transfer switch makes switching from utility to generator power as easy as possible, and can also run some stuff in your house if you want. Also, the transfer switch is totally upgradeable if you decide in the future to get an automatic generator. I don't know of any Generac (and they are a world leader) generator that can kick on automatically, other than there whole home automated generators. However, with the transfer switch, other than starting the generator - that's all the work that a 5500 requires. You can purchase smart battery back-ups for computers that connect wirelessly to the internet, and will notify you in the event power goes out. I have my router and modem connected to one, so that if power goes out, I still have internet access enough for the back-up to notify me, so that I can make arrangements to get my generator up and running. While this is likely more than you wanted to spend - it beats spending 3k+ on a whole home automatic unit, and offers much of the same reliability and ease of use.
As for having a Generac non-automated whole home unit kick on, we install and maintain Generac generators and I am not aware of that feature being possible on anything other than whole home automated units. In fact, any of the standard generators require a pull start, or switch to start. The rapid start system is much easier than traditional generators, and either requires one or two good pulls to start, or turning a switch if it has electric start. Even the new transfer switch doesn't have the ability to start the generator automatically in an outage.