I ride a kilo tt, and like they said there isnt much you can get for 500$, youre better of saving your money to build a better bike. right now im building up a leader 725 during the summer and after pricing it all out its about 800$ for everything. BD bikes dont require that much assembly, it takes probably 1 hour if you dont know what youre doing, all you need are the right tools (a bunch of hex wrenches) and knowledge of how to set up brakes (youtube).

Back on your current question, it depends on what kind of pedals you have, most of (all of ) XLC seems to be mostly platform and mountain bike style pedals. I know that straps like YNOTs or HoldFast need bmx style pedals but im sure mountain bike pedals will suffice just as well, though these are around 50-60$. Right now I've changed from YNOTs to straps and cages which are cheaper if you dont have to buy new pedals to with them, both offer a good amount of holding in, but after riding for a so long with foot retention i've found that I actually feel unsafe when i ride bikes without it since I slipped off a set of old pedals before and put a nice gash into my calf.