I combined the play sink and play stove into a one-piece kitchen by having them share a side. I found a bathroom faucet at my local Habitat ReStore for $15 (and that included a sink I didn't even need!). Time investment does not include painting.
Here's my cost breakdown.
Lumber: $25 (I used some scraps.)
Dog bowl: $7
Primer and paint: $19
Prepping dinner while my toddler works in his play kitchen beside me: Priceless.