Hi Gracious86 and welcome aboard, the mower looks to be in a well cared for condition. The fact that it was given to you tells you it's worth. More pictures would help to ascertain its mechanical condition, a few pictures of the chains and sprockets hiding behind the chain case is necessary as is the cutting reel.

Below is a link to some information on the 45 models

https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=64934

If you type your Scott Bonnar into the search field at the top of the page you will find a lot more information of interest. Once again welcome :-)