EFI is doable for somewhere around $500 and up for a custom tunable system. That means something that would not just run OK, but that can be tweaked to maximize performance and mileage. Note there are many variables that would dictate the final cost; not the least of which is your willingness to learn and do more of the setup yourself.
There are two common routes (besides expensive packaged kits). You could either use a hacked complete factory system (free to a couple hundred maybe) and a couple hundred in software to tune it. Or, you can use an aftermarket ECM ($200-300) and whatever you want for the peripheral parts and wiring (for better performance and/or lower cost), and free or cheap tuning software. Both choices require gaining knowledge and fabrication skills. The factory system will require more knowledge and research with less fab, and the custom system has the potential to perform better in all regards, but may need better fab skills depending on your choices. Remember, these are general statements.
So, the question becomes - How willing are you to learn what EFI is and do more or less of the work yourself? If you want to learn all about it and handle fabrication and fitting on your own - cheap. If you're not willing, that's what $2000+ kits are for, that suit folks that don't want to know or figure stuff out - they just want to bolt-on and go. Where do you fall in this picture?
David