Something to consider on cost..... You can get a HVLP spray gun for less than 15 bucks. Cheap enough you can just throw away after the first use. I've found the cheapo's good enough to use for paints like two part epoxy or urethane that are annoying to clean up. Just throw the whole thing away and get another. For each coat if necessary. Of course you also have to have a compressed air source with plenty of CFM flow (the HV part of HVLP)

I have an expensive cup sprayer, and though it does spray better and is easier to disassemble and clean, the cheapo's save time and mess. That being said, I spray lacquer with my expensive cup sprayer, because for me lacquer is so easy to spray and clean up afterward. It drys fast and you don't have to wait long periods to do multiple coats. But lacquer is hard to find, especially in any decent color selection. There are some relatively cheap enamels that you can find at a auto paint supplier that will be a better finish than lacquer, but take longer between coats and to dry for use.

Some will say don't clear coat a powder coated frame. But why not. If you scratch or ding the powder coat then that's not an easy fix. But with a good clear coat over the entire frame, the scratch or ding will likely just be in the clear and it can be sanded out and clear coated again easily. That is one of the reasons they clear coat cars. I think UV protection might be another.

Of course you mentioned cost for you budget on this project. And if this is the only time you'll be doing something like this then yes your spray cans were likely the way to go. But if you see yourself doing more painting projects of any sort.... consider getting the equipment to free your self from spray cans.