@OP, Doing it yourself or paying someone?
In principle spoke reuse is fine if none are showing obvious damage, but unless hub dimensions and rim ERD are the same you would probably be making life harder for yourself/whoever. Possibly worth keeping for a later build however. If you’re pretty consistent in hub choice certain spoke sizes just keep coming up.
UK retail on spokes is pretty high although most shops building will do a drastic reduction from what they’d normally sell spokes for if you’re getting them as part of a build. If buying spokes yourself probably cyclebasket in Wales for ACI or Rose in Germany for DT are usually the best prices. Most builders prefer to do their own calculations for spoke length though – you can get a wheel out of less than ideal spoke lengths but it’s s lot more hassle and they’re the ones selling time.