Creating custom search is not the easiest of tasks for beginners. You will need templates search.php and searchform.php – View Codex. You can then edit searchform.php and add any fields you need. When the user submits the form it will also add any extra fields you have – so your search url may look something like this /?s=1000&num=5&type=years (using the Loan Form example given in the question).
Once you have your form set up and submitting correctly you can use a hook such as pre_get_posts – View Codex combined with some Conditional Tags to test if is_search() then you can grab your extra inputs: $_GET['num'] $_GET['type'] and modify your query based on the values given.
That’s the gist of it anyway.