Add small feature to Joomla componetn

Need to add "discount" feature to my existing web site. I have Joomla 3.3 and EventBooking component 1.6.4 I need to ad feature to my site. Now, In back end i can create event and set up price for it. Discount feature exist, but only for registered users. I want to create it for everyone. For example In back end i will add price, discount and field "new price" will be calculated automatically based on old price minus discount (in %). On front page all users should see old price (is strikeout) , new price (marked with red) and discount (amount in %) and word "discount". Word "discount" for front page should be taken from EventBooking DB (to keep multilingual feature going). After work, I need report where all changes will be show (File name, what added, what was deleted, changes in DB ).