I don’t really know an affordable way to make it more secure
Basic car alarm goes a long way. Not only will it make a racket if they break in, but if it’s installed properly, it will also disable the ignition, making it take much longer to get started. Most joyriders and opportunistic thieves will move on. Decent alarm should be in the 200-300USD range and it may reduce your insurance by that much or more.
Nothing is going to protect it 100%, you’re just trying to make it harder to steal than the car across the street.
That should be the installed price. There’s 100-200 in equipment and 1-2 hours shop time. Finding a competent shop is sometimes the tricky part tho.
Hell, I’d bet a local car audio shop would put you in a hidden ignition kill switch for less than $200. I installed thousands of them in the 90’s before immobilizers were semi-standard.