I think it's in the 1e DMG that Gygax says the PHB prices are Alaskan Gold Rush economics, with $5 eggs. A lot of the PHB gold piece prices are quite close to historical silver piece (eg shilling) prices, so that's one way to go. Gygax's stated preference is to assume a highly inflated economy right off. The problem with this is that (a) it only works for a Castle Greyhawk type setup and (b) his mundane NPC wages are mostly set off an historical silver based economy, though some of the expert NPCs are on the inflated gold based economy.
Over the years since 3e WoTC has kludged it by lowering the value of a gp back to 10 silvers while also reducing low level treasure hoards & increasing NPC wages, but the gap is a bit too big to be crossed IME - eg a normal sword should be more like 15 silver than 15 gold. Pathfinder 2e bit the bullet and went over to silver-based and gold worth x10.
My preference is to stick with the kludge, remember the PHB prices are an inflated near-maximum, goods may often be bought for a lot less (especially by NPCs!), and increase NPC wages somewhat. Basically the WoTC approach.
I use 1 gp = 10 sp, cheap food for a day 1 sp, poor daily wage 2 sp, good daily wage 4 sp. An sp is worth about $10 and a gp about $100. Players pay either the PHB inflated prices, or can bargain for lower prices - NPCs are probably paying 1/3 to 1/2 PHB prices on most goods.
Adapted from 5e DMG, but I use this in my 1e/OSRIC game too:
Social status Income & Expenditure
Lower Class
Subsistence 1sp/day, 3gp/month Maid, Scullion, Slave
Poor 2sp/day, 6gp/month Labourer, Cook, Infantry Soldier, Barmaid
Unassuming 3sp/day, 9gp/month Yeoman farmer, Corporal, Longbowman, Cavalry, Sailor
Decent 5sp/day 15gp/month Sergeant, Heavy cavalry,Tailor
Middle Class
Modest 1gp/day, 30gp/month Adventurer, Lieutenant, Innkeep, Reeve
Comfortable 2gp/day 60gp/month Armourer, Master Smith, wealthy Innkeep, Captain
Upper Class
Wealthy 4gp/day 120gp/month wealthy Merchant, Colonel, Lord/Lady
Aristocratic 10gp/day 300gp/month High Priest, Baron, General
Noble 20gp/day 600gp/month Duke
Royal 40gp/day 1200gp/month King
Imperial 80gp/day 2400gp/month Emperor
For XP, in my 1e/OSRIC game I keep 1 gp = 1 XP, but I reduce gem & jewelry values a lot from the 1e DMG listings, to about 1/10, and I'll reduce gp in treasure if it looks excessive. I'll also reduce some magic item sale values - and thus XP - to about 1/10 the 1e DMG list values. In compensation I give increased monster XP, and lots of XP for non-combat achievements, but I keep big piles of gold as an adventuring lure.