Alright, so I have a Vilano aluminum road bike with 700c tires. I live in a town near Austin, Tx. I'm not 100% on any laws, but a quick search said I can't go more then 20mph on electric only. I'm not sure how I can achieve this. Maybe assist only? Do I need insurance? I don't ride much. I've maybe put 30 miles on the bike. I usually ride around 5 miles and after that I'm fried. I'm looking into commuting on it to work. (add racks n lights for backpack n such) It's 10~miles each way. But the only way I would ever do this is, if it was an E-bike. My thought is that the 700c tires have low rolling resistance so it should be more power efficient then bikes with fat tires. But I wonder about achievable tire mileage I can get. If it works well, I would like to transfer to a nicer bike. I'm not that into bikes, but some of the $600~ Trek bikes look nice. Maybe If it was a mid drive, I could get a bike with suspension and wider tires if needed. I'd like to actually be able to do 20mph+ but I don't know about legal stuff. I've done 26mph full out on it as it is, but I've been down to 6mph in a wind. I'm also trying to compare this cost wise, to a Honda PCX 150.

Essentially I'm wondering how much I could be looking at to convert my bike to a decent E-bike. A hub setup could be in the $700 range and a mid-drive setup could be over $1000, which sounds like a LOT. Just some more rambling down below.
My main question about price is the battery. Lipo packs, buy a pack, or make your own out of 18650 or similar batteries. It being detachable would be good too, so it's not sitting outside in the 100F+ heat. I don't have definite prices for building one, but it looks like it could be done for $300, but I'm not sure how good of a battery that is. There are Turnigy lipos packs, 6s 20AH 12c, could get 2 for about $400 and run them in series. I already have a lipo charger/balancer. I've seen prebuilt packs for $800, Luna has some for $600~... Then there are mid-drive and hub motors. I would think a rear hub motor would be better then a front. But I worry about life span and actual performance. But it seems to be far cheaper than a mid-drive.

Thanks for any input,
Awaqa909