Ceremony and Reception in the same place?

Generally speaking, one venue should be cheaper than two but that depends on location and the type of venue. If you have it in two different places there are also transportation logistics to consider as well. I would encourage you to do some research on venues to get a feel for what is available in the area where you would like to get married.

Some venues charge extra to get married there.

Usually, yes, but it varies. But many ceremony sites aren't super expensive. For example, I had my ceremony in the garden of a park, and it was only around $500 to have the ceremony there. Our reception was a few miles down the road, and we could have had our ceremony there for no extra charge except chair rental, but they wouldn't let us start at the time we wanted.

You'll have to ask each venue. There are some venues I thought that I could make work within my budget only to find out they charge an extra $500 to do a ceremony onsite. I ended up finding one place that will let me have the ceremony for free, but it took a lot of research and I'm not sure it's the place I'll go with. So just keep looking and asking!

It depends. I've seen ceremony charges of 200 or 2000 at reception sites - usually the convenience is worth something. But if you love a reception site but they charge an extra 1500 for a ceremony, and your church a mile away does ceremonies for 100.....meh.