I bought some barley straw in the summer when they didn't think they'd be getting any harvest at all and it was £3.50! Don't think it's much different now; sorry, don't know about wheat.
A lot of it is personal preference or how your stables work. Years ago, barley was frowned upon as it still had 'ears' but combining is different now. There is also oat straw which can be similar but horses can like to eat it more than the others. I prefer barley, it suits my boxes and seems more absorbent.
Barley is softer. The stuff we have almost feels like shredded crepe paper. Lovely fluffy and soft.
Some of the oat straw we've had has been very grey and stick like. Horrid. Hated it. I know which I'd rather lie down on, if I had to sleep in a stable.
Never bought it in small bales. We buy half tonne bales and pay per tonnage when the lorry's trailer is weighed on a weighbridge.
I only pay 65p per small bale at my yard (wheat straw). YOs said it was not good quality this year so therefore cheap but all my straw so far has been fine
On yard we pay £2 per bale straw ( small) of which most is nice but some is clumpy and smells musty. Think most of it is barley but we have had oat in the past so could be a mixture of the two.
Hay (small bale) grown, cut and baled on the yard is now £3 a bale this year couldn't quite work out why it has gone up by 50p since we are still using previous year's hay and the new stuff hasn't even been touched yet.