$US1000.00!! - that's a fortune
For me that's the sort of budget I dream about Rezso. Then I tend to use high levels of reclaimed and recycled materials in my builds with the actual engine kit itself being the main expense.
Building my Hercules tricycle was the only time I really pushed the boat out and spent money and that was $NZ250.00 for a 250watt motorwheel kit, $NZ200.00 for a secondhand near new condition Indian made Hercules heavyweight bicycle and $NZ150.00 for a tricycle axle kit. All the other parts for the build were drawn from my pile of bike parts most of which came from the council tip.
My present faux Rudge autocycle is also going to be a cheap build. The 66cc/80cc gen II China Girl kit cost me just over $NZ200.00. One tatty old but complete 1950's gents Rudge sports bicycle $NZ100.00. Two NOS mudguards at $NZ20.00 each. One Mixte frame free from the council tip and the rest as usual is all reclaimed bits and pieces that also cost me nothing.
It looks like buying repop Rudge transfers/decals and a repop 'Brooks' saddle badge from England will cost me about what I paid for the whole Rudge gents bicycle, but that's Ok because I want my bike to look nice.
Some forum members have spent thousands of dollars on their bike builds, - which is fine, - but really the final build cost will come down to how much you want to do yourself, how much free material you can find and the actual build spec that you want to work to.