The market average rate for a 100x200mm concrete mowing strip is around $20 per metre. Going for a smaller dimension won't reduce the cost much as the cost of digging and formwork stays pretty constant.
I think that's not going to work out too well for a domestic job of say 50m and expectation it'll only cost $1k.
I'd suggest that for about that (50M) then cost would be at least double that.
OTOH if you had a trailer, a small concrete mixer, and some timber to use for boxing, you'd be able to DIY for about $4 / metre (& sweat).
Ive got a trailer, can hire a mixer or manually in wheelbarrow, but my concern is my finish. Extruded looks great but no reinforcing. I woudn't trust my own finish nor the sharpe edges, even with those edge tools.
Im now thinking to trench myself and use quickcrete for a 75mm reinforced base. Then mortar 200mm x 100mm x 40mm pavers on. $1-20 each, so per metre that as cheap as the timber, plus quickcrete.
Getting a good float finish on concrete isn't too hard - it mainly seems to be a question of timing (waiting until it's at the right stage of setting after pouring), then not getting too fussy and over-working it because there's a little flaw that you think needs to be taken out - but in reality you're only seeing it because you're on your knees looking closely.