I scour the gun shops and pawn shops for used, heavy barreled rifles. These can usually be found in pretty good shape at fair prices.
The last two I bought were $500 each and had seen little to no use and certainly no abuse. A Win70 HVB .243 was in excellent condition and a Savage 112 BVSS .300WinMag was in very good condition. I talked to both of the previous owners, the .243 had seen about 40 rounds and the .300, about a 100 rds.
I put an older Nikon Monarch UCC 6.5-20X44 AO with fine crosshairs that I bought years earlier on the .243 mated with Leupold Long Range STD base and Burris Signature rings. I have the trigger adjusted down to 2lbs and with less than $1000.00 invested it has produces groups of 2.5-3" groups at 500yds with handloads, quiet regularly.
On the Savage .300 I mounted a Nikon Buckmaster 6-18X40 with side parallex adjustment and Target Dot in Burris Rings/Mounts. This is the pre-Accu-Trigger, so I added a Rifle Basix trigger set at 2lbs. Again, roughly a $1000.00 investment and accuracy is right at 3" at 500yds. I took this rifle to the range (Red Cloud) at Fort Stewart, Ga. and took it out to 1000yds. I was shooting at a mound of hard Georgia red clay but could easily see my hits and with a little adjustment of my range card (derived from JBM) I was stacking 'em on top of each other.
500yds is doable and doesn't have to break your bank.