$450 - $500 should get you one in excellent or close to it condition. No accessories though.
A No5 bayo in excellent shape and British Made, can cost almost as much as the rifle.
For a VG or better, the average price seems to be around $400.
95% or better are difficult to find and most people won't let them go for under $450.
New in grease rifles will bring as much as $650. A wrapped rifle will go for $1000 or more.
For the type of money you're willing to spend, the rifle should be in the 95% bracket at least with a perfect bore, no cracks or scrapes and maybe the odd storage rack handling ding.
There are a lot of No5 out there. Most have been used and show it. Many were varnished/lacquered for service in tropical areas.
Laidler made a comment that in Malaysia, they removed the metal nose caps on some of the fore stocks and rounded off the wood. The caps collected coastal salt marsh water and rusted badly, ruining the wood underneath.
Know what you're looking for before you buy. Go to the gun shows in your area or post your want on the EE here.
Just understand, everyone here has bought a story at one time or another. I have and likely will again. It's a pitfall of the hobby. None of us are fully immune and at times, it can be embarrassing as well as sad.
All I'm saying, is you're new to No5s. Check out different sites for commercial pricing to see what you're up against.
Don't be impatient. The right rifle, unlike the right girl, will come along.