DD's parties age 1 through age 7 were BIG parties! We were very active in our playgroup and parent/infant classes and then school. We always invited everyone we knew and the whole family. We spent less than $100 by choosing the time to be between meals and having it at a public park and by making the cake myself and giving a single item as the favor (kids only).
Party for age 8 was for 8 girls total in our house. Still spent the same amount and spent the same amount of time planning and preparing. 8 girls versus 30-100 people = same cost. Why? Food. Favors were free because I already had the fabric and I sewed each guest an apron. Since it was for 8 and in our home, I decided to do a lunch. The girls were really into "cooking" themselves, so I provided all the fixings for them to prepare and eat their own lunch. Decorations were things we made, except I did order and buy a small balloon bouquet. (I do that every year, so it was the food that made the difference.)
This year is her 9th birthday and it is a slumber party for four girls total. Food is the only cost. We're doing balloons blown up by us this year specifically for a backyard game where helium balloons wouldn't work. Favor is a poster the girls will be creating with my scrapbooking supplies. The pictures will be printed at a local place in an hour (inexpensive, but the only other cost besides food).
We've had themes every year (big or small). My budget is always a self-imposed $100. I could have always done big parties for $100. I was good at it.
However, our guest list kept growing and growing and growing. By age 7, we knew families from so many sources. I didn't want to cut the guest list by asking parents to drop off only the invited child in a park. I was always so busy photographing the party and keeping the party moving along that actually watching the children had to be done by their own parent(s). Moving it to a location where I *could* watch all the children and keeping it frugal meant our home. Our home is small. Our table seats 8. Dinner parties have always been for 8 total. We simply do not have space for anymore unless we can seat 4-6 outside. Not always possible in late March. This year's slumber party is four girls total due to space. That is what will fit in our DD's bedroom or the living room. We don't have a larger space. Sure makes the guest list decision a lot easier! 
Party for age 8 was for 8 girls total in our house. Still spent the same amount and spent the same amount of time planning and preparing. 8 girls versus 30-100 people = same cost. Why? Food. Favors were free because I already had the fabric and I sewed each guest an apron. Since it was for 8 and in our home, I decided to do a lunch. The girls were really into "cooking" themselves, so I provided all the fixings for them to prepare and eat their own lunch. Decorations were things we made, except I did order and buy a small balloon bouquet. (I do that every year, so it was the food that made the difference.)
This year is her 9th birthday and it is a slumber party for four girls total. Food is the only cost. We're doing balloons blown up by us this year specifically for a backyard game where helium balloons wouldn't work. Favor is a poster the girls will be creating with my scrapbooking supplies. The pictures will be printed at a local place in an hour (inexpensive, but the only other cost besides food).
We've had themes every year (big or small). My budget is always a self-imposed $100. I could have always done big parties for $100. I was good at it.
However, our guest list kept growing and growing and growing. By age 7, we knew families from so many sources. I didn't want to cut the guest list by asking parents to drop off only the invited child in a park. I was always so busy photographing the party and keeping the party moving along that actually watching the children had to be done by their own parent(s). Moving it to a location where I *could* watch all the children and keeping it frugal meant our home. Our home is small. Our table seats 8. Dinner parties have always been for 8 total. We simply do not have space for anymore unless we can seat 4-6 outside. Not always possible in late March. This year's slumber party is four girls total due to space. That is what will fit in our DD's bedroom or the living room. We don't have a larger space. Sure makes the guest list decision a lot easier! 
