My son and family have booked a villa in Tias in July. Can anyone tell me a bit about Tias - supermarkets, bars, resaurants and also the average cost of things.

You are in the wrong section!! Tias is above Puerto del carmen which might explain why noone has posted any answers for you.
Tias is a nice little town, ithas a good selection of restraunts and is a five min bus or taxi journey away from the hubbub of PDC.
to give you a quick list of eating and drinking places-
tapas - el Correos and la ermita
restraunts, las vinas, iguaden, chino, el rincon de pasta plus others
one english bar, numerous small snack type bars which do pizzas and take away burgers etc.
good selection of supermarkets, grocers and butchers.

san antonio bakery is good for snacks pastries etc.

theres a few clothes shops jewellers etc but for real tourist "stuff" youd need to go down the hill to PDC.

From the high street you can jump on a bus or grab a taxi pretty much anytime, buses go a couple of times every hour, one at 20 past and one at 20 to, they stop at biosphera which is the shopping centre in the old town.

Youll be fine. Cost wise not sure what you mean?? Cheaper than PDC but not as cheap as the really rural areas.

That’s assuming you’re actually in the ‘town’ of Tias and not the region – just occasionally the region is quoted as the villa location and if that were the case then it might be in the town of Puerto Del Carmen – Unlikely but worth checking up if you’re unsure, and I guess thay maybe you are by posting in this section – however way you look at it though Tias is not the same location as Costa Teguise.
Ole

We've started exploring Tias - and it's very nice.

We really liked El Rincon de la Pasta. (Downhill off the main street). Family owned restaurant that used to be in San Bartolome.

We thought Iguaden was ok. (Main street). Not rushing back, but wouldn't refuse to go there. If you know what I mean.

There are two restaurants on the southern end of the main street, on the roundabout. Went in one of them and it was the worst restaurant I've ever been to on Lanzarote. Then several bods said don't use either of them.

Oscars bar is very nice. (Southern end of the main street). Relaxed and easy going. They have Connect 4 dotted about if you have kids with you.

A new sports bar had just opened very near the central roundabout. Didn't look in, but they do have a decent sized 1st floor sun terrace. I expect it will be very nice to watch the sunset from.

It's all pretty walkable. Explore & enjoy.