I'm all about saving money on a wedding but one thing you never want to skimp on is your sound system. If people can't hear then it will dramatically effect the enjoyment of the wedding. Do your homework and make sure you have someone in charge of sound that knows what they are doing. If possible you want your sound person and your sound system set up and properly checked during the rehearsal the day before. Don't try to "wing it" on the day of the ceremony. That is a risk you do not want to take.
During the ceremony you want to ensure the officiant is mic'd and when the groom or bride speaks they officiant needs to hold the mic by their mouths so the guests can hear everything clearly. Don't expect your voices to project well enough without a mic, it won't happen. You need proper amplification. This is especially true if you are getting married outside. Your voices will not be able to compete with the background noise or be able to carry all the way to the back row of your guests.
The reception is even more complicated when it comes to sound. You have speeches, toasts, comments from the crowd, games and dancing. Your sounds system needs to be able to handle all those situations and even more important, your sound person needs to have to skill to adjust for each part of the night. You might not think so right now but your sound person plays a huge roll in the success of the wedding. Please put someone very talented in this position and give them the gear they need to do well.
If you're looking to rent equipment these guys have absolutely everything you could need: SW Event Technology.
Please take my word for it. I've been at weddings were the sound person struggled and the frustration the guests felt when they couldn't hear was hard to watch. This is one of the biggest days of your life. Make sure your loved ones can hear every magical part of it.