I use several Mini-Circuits ZQL-1900MLN pre-amps for that range.
This list price ( new ) is $265.
BUT ...... you can find them on ebay for less than $100.
I see one on there now for around $89 new.
Even though the specs are for 1850-1910 MHz, they perform very well down to around 450 MHz.
Around 700-800 MHz the noise figure is close to 1.0 dB and gain is around 28 dB.
Here's a test of one of mine.
This is what the amp looks like:
You can find the specs (in PDF format) can be found here:
www.directdatasheet.com/part_detail.php?part=ZQL-1900MLN&mfg=MINI-CIRCUITS
Rich
Some additional spare pre-amps.