My experience is quite similar. Here I post a feed back I've got once from the advertiser (and that job was posted for quite short time - I can't say exactly how long, but certainly shorter than most of the offers):
Here are all the responses. The first column is USD, the second column
is Months. The "x" indicates no information, but the person did offer
helpful advice.
5500 3
1200 0.5
9200 ?
4500 4
1920 1
3500 1.2
2500 1.2
15000 6
x x
x x
9000 1.2
x x
x x
1000 0.5
3500 1
2500 0.5
1000 1
12000 1
5000 1
2500 1
1000 1.2
4000 2
7000 1.2
x x
3000 3
x x
4000 x
4000 x
7800 1
2700 1
x x
3500 2
15000 2.5
2100 1
2500 2
x x
8000 2
4350 1
x x
5635 1
x 2.2
5000 2
2500 2
15000 x
15000
5000 2.5
4000 1
1500 1
1000 1
7500 0.75
8000 1
6800 2
2250 1
20000 3
2500 3
900 0.75
Mine bid was the last one. It is possible that it was rejected because it was to low and did not look serious. Actually being rejected so many times I bided much lower - just to test if there can be any possibillity of geting such a contract.