You can barely fit Audi A3 in that budget for 5 year old model and that I assume it gonna come with 100k on the clock that will defeat your number one priority of being reliable. For smallest BMW 3 series you got to push for 6 years model, again not worth it in your scenario.
Hi Joyce, welcome to the right place for such advise. Take what is relevant and leave what is not as sometime people get bit carried away on such opinionated thread here. In short none of the three brand you suggested for new car offer anything within your suggested range. You are better off with the little bit used car and your best bet is to go Japanese or Korean considering the budget and reliability is on your top priority.
I am driving 9 year old Touareg with no problems in past, and get car regular service and maintain with good workshop. Instead of limiting to 3 years with low budget you will restrict to masses brand only and not good European or German Cars.