Design challenges now

I believe, today, it is possible to submit Design Challenge with total costs only 1350 design coins. 

Note: Small Fire Station Lvl.1 has capacity 50 (health and police have more.) and some services are provided free at the beginning.

GreenValley  home lvl.4 has demand 5 and population 356, so you just need to fit 10 of these homes , and you get total population 10x 356=3 560.  That population is sufficient to Submit the design challenge. 

Costs:

3x Deluxe Wind Power Plant lvl.1  = 3 x 200 = 600 coins

1x Water Pumping Station lvl.1 = 750 coins 

No service upgrades needed and total  costs  are 600+750=1350 design coins.

I guess, I do not understand what is  your problem.

As i designed the hyppe Lifestyle challange  I have build 4 frostfjord buildings and upgraded they to level 6. Therefore i spend around  11,5k design coins for the nessesscary services and earned for the 4 full upgraded  buildings around 4k which makes a expenditure on 7,5k. But i need more for replace too a nice road. So i scrapped the buildings and build they again but without expenditure but with earnings of 1k for each new upgraded building to level 6.

Basically the way to do it is to build 3 regular residential buildings. They will meet 17,500 population in order to submit. You need to fully upgrade 2 but you don’t need the last upgrade on the 3rd. You still need to upgrade utilities, but there are enough coins to do the upgrades. I don’t like having to worry about utility upgrades in design challenge but it is possible. 

Yes but the bonus points you need 17500 population which requires more services.

Also it means it's much harder to use fancy roads to get better scores.

Current challenge I used all landscape for a pretty pic & losing points so I drop from #2 which mean even less rewards etc.

I did the same but after rebuilding once the services on 10 buildings needed upgrading the second time. Spring city was the worst requiring way more services.

It's supposed to be a creative challenge not big ugly service buildings ruining the look of it.

I use only 2 small fire, 2 small police and 2 small health  buildings. This gives an area of 2 x 200 demands where i can build e.g. 4 full upgraded region houses.with gives a total of 180 demands. You can push up the population e.g. with parks, entertainment.  If it is a very small card like the frosty fjords I build only houses for one area. The other needed service i built on the sides where they will not been seen.