Thanks @Emilyelizaphoto really like your profile by the way, smashing photos and great reviews.
So for the sake of argument let's say you're comfortable paying 10% of whatever your Thumbtack revenue is to Thumbtack for supplying you the leads that enable you to generate that revenue. I use 10% myself, you're might be more or less but you'll be able to work the figures out for yourself.
That means to get a customer worth $1000 in revenue you don't want to pay Thumbtack any more that $100 for supplying you with the leads that you needed to get that customer.
Your close rate is 1:5 = 20% ... 20% of $100 is $20 so your sweet spot for that kind of job is $20.
You're currently paying $35 for each of 5 leads to get $1000 worth of business. So you are effectively paying Thumbtack a 'finders fee' of ($35 x 5)/$1000 = 17.5% - you might be OK with that, you might not in which case raise the issue with Thumbtack and see what they can do to reduce the cost per lead of your low end leads.
To get a customer worth $2500 in revenue you don't want to pay Thumbtack any more that $250 for supplying you with the leads that you needed to get that customer.
Your close rate is 1:5 = 20% ... 20% of $250 is $50 so your sweet spot for that kind of job is $50.
You're currently paying $49 your high end $2500 leads ... that's a fair value.
You're getting a better ROI with your high end leads than your low end leads.
You were doing brilliant at 1/5 ... I wish my close rates were as good as that.
2/18 isn't good but it's closer to what I've been doing. 2/18 is roughly 1 in 10 which is where I'm at. I really hope that February/March were just a blip for you and that you have some better months ahead so that you get back on track at 1/5 for the year. If April/May are just as bad then this close rate might be your new norm. If that happens you need to figure out what you think you should be paying to get the ROI you need and then raise that issue here in the hope that something could be done to reduce you cost per lead.